The .NET Framework version 4.5.1 introduced a generic version for Marshal.PtrToStructure, which opens up the possibility to act not only on a specific structure, but on all structures, thuseliminating the need for an explicit cast. Union-Ized? If the caller can not ensure non-null input, this must be caught there. Since every field in the union shares the exact same memory location, any time one of the fields gets assigned a value, all other fields previously assigned values are overwritten. In the Interpreter class I've created a couple worker routines for reading and writing ProductionItems to/from FRAM: Finally I have two interpreter commands to test the functionality: These are the blocks of code executed in the interpreter when the user enters the "testitemsave/load" commands into a console. Learn more about Stack Overflow the company, and our products. My objective is to convert obj to byte array and read it through the implementation of Read trait. If on .NET Core 2.1 or above then one can rely on the native, MemoryMarshal is not exists in old framework:\, Unmanaged byte array to managed structure, Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. Im a C n00b and just came across unions and this name.variable stuff in some code I was looking at, which I didnt understand and didnt yet bother to look into, and then BAM! bornach has updated components for the project titled Rainbow LED Effects using PWM Generated by OpAmps. Just take care during your order of initialization since the C# rule about every field of a struct must be initialized is still enforced for an explicit struct. Hi, Here is a structure of single tile in map: A game map contains exactly 2016 tiles. sizes. If it is a managed process there are surely far better ways of inter-process communication http://stackoverflow.com/questions/13418795/convert-byte-array-to-structure-in-the-compact-framework. From the outside, they look and behave just like a struct, and are in fact declared, initialized and accessed the exact same way. So to turn our struct sensor_data into a union, we simply have to change the keyword and we are done. If memory is super tight etc etc I can see why you would do that. Be super careful when using bitfields- when a bitfield overlaps a storage unit boundary, the behavior is implementation defined AKA: NOT PORTABLE. In the overall architecture, a new "hyper-convergence" concept was Hi, I have a python app that i want to be able to get variables from a php page on my webserver. So please any one can help me by telling How to convert a struct object into an byte array.. Here is the definition of Intels IA32_MC7_STATUS register: Using the above named fields is far easier to read and maintain, and removes worry about which bits are being manipulated. Could you please show me why and how you convert a unmanaged structure to a managed byte array? (Apparently, the ones listed in the quote belong to so-called special classes.) The same principle used to extract a byte works also the other way around, and we can use unions to concatenate integers. Private Structure MyStruct Every register access in world of PIC programming using XC8 uses the combination of register bitfields in struct unionized with name of register. Which am doing using marshalling as below: C#. i do this with a lot of serialization code but you have to be careful transporting them between different architectures. =P But I believe you've hit the main problem so I'll try to get memcpy working, unless you can suggest a better way to return the new ProductionItem instance from memory. Once initialized, we can access each individual field the same way we just assigned values to it. I have to send a structure through TCPClient socket. With a union, all three fields will be located at address 0x1000. So far so good, but when i stress the system by sending thousands of events (~20000) per second, The original method (ConvertBytesToStructure) getting poor performance, and the new method getting excellent performance.. Here we have a 32-bit integer overlapping with an array of four 8-bit integers. Notrly, the first 2 vars are printed in decimal, then that last one is in hex so to keep the output clear they prefix the hex with 0x, Thats correct given that the printf is not formatting the data as hex. The function is expecting a uint64_t, but it really isnt one as it is a packed bit field. The only blunder I had was changing a parameter into a pointer and not accounting for that when measuring the size of the data buffer. How to copy QByteArray to another QByteArray with specified size? As follow-on advice: use the native register size [unsigned] int whenever youre not dealing with a value range which is precisely the 2^sizeof(short) or 2^sizeof(char). Connect and share knowledge within a single location that is structured and easy to search. Thank you I may try this if I cannot get the simple casting to work as I thought it should.
Other than adding the bit length, bitfields are still just structs, and are therefore handled as if they were just any other regular struct. My problem (spelled failure) is with the Introduction: But this is not how I want to send it to the Server Socket. : HaD has a post on this very topic just in time! If you are looking for information about Qt related issue register and post your question. We can't convert a bytes array to a structure which contains managed type. Here is my code. Yes, there are appropriate times and places to use unions and structs, but to diss them wholesale is bogus; I use these constructs as necessary, not on a whim. :-P. I guess the tracker on my PC isnt working correctly; I could have used some help on structs about a month ago. }; Thatd allow for a number of common C data types, with a struct member that defines which of those union members is relevant and how to interpret it. Once again, no size determination nor expensive copying is required. The next code snippet addresses this shortcoming. Quite similar to the union option tbh, with both some small pros and cons. Here is my function to convert bytes into struct: static GameMap GetMap(byte[] data) { unsafe { fixed (byte* map = &data[0]) { return * (GameMap*)map; } } } I am using pointers, since performance is very important in my case - game map will be read at least 100 times per second. Learn more about data programming at bytecomb.com, http://msdn.microsoft.com/en-us/library/4ca6d5z7.aspx, http://www.codeproject.com/Articles/25896/Reading-Unmanaged-Data-Into-Structures, That method I am using is about 70x faster than. Why is this screw on the wing of DASH-8 Q400 sticking out, is it safe? uint16_t cal_z; You should make len a parameter of those methods and pass it in from the caller which actually knows the size of the data structures you are trying to write/read. messageStruct.hdr2 = 0
Ideally, it would be generic, so that it doesn't have to be hand coded for each different structure . Advantage of AntDB: hyper-convergence + streaming processing engine Some compilers might work beyond the spec to allow packing into unsigned chars, and short ints, etc. However, they need to be used sensibly. How to use http requests (Get function) to get variable value? . It creates a type alias; byte becomes another name for the type unsigned char. So for example I can access a bit in a port using PORTABits.RA0 or write to entire port with PORTA. Suppose I have a structure Learn more, Unionize Your Variables An Introduction To Advanced Data Types In C, IEEE 754 single-precision floating-point numbers, https://msdn.microsoft.com/en-us/library/windows/desktop/ms738571(v=vs.85), This Week In Security: Barracuda, Zyxel, And The Backdoor. So you replaced an union with explicit type conversion, which does exactly the same thing but without word union. Return CType(l.ToArray(GetType(Byte())), Byte()). I update my little program based of your answer to benchmark it. jpgs/bitmaps) within strings, and I need to sometimes convert these This is overly complicated, as the involved slow copy operation is unnecessary in most cases (as is the call to the SizeOf method). Too many variables as well. You might want to experiment a bit and try running a similar test with a larger struct; maybe your method is faster for the specific problem that you're trying to solve. and the other involved casting a char* : c++ - Convert struct into bytes - Stack Overflow. Ive never seen bitfields in C.. Can anyone give an example which IDE for microcontrollers (PIC,AVR,MSP430) supports that? Converting 51.508131 or -0.128002 to ints gives 5150 and -128. So first try to just save it in a random char array, and get it back in a new structure and see if that works. The struct I need to convert to byte array and add the Read impl. It consumes less CPU power and memory than JSON but still preserves the field names . How do I copy &[u8] to another &mut [u8] which is a vec. I am trying to implement std::io::Read trait for a struct. Unio-Nized? Qt Centre is a community site devoted to programming in C++ using the Qt framework. Now JSON or XML? Now the dispatcher can check those first values (due to same begining of stuctures they are always at the same memory addresses), cast the rest in the correct structure and call the needed function. Sign in to post your reply or Sign up for a free account. My python app is on my computer. Maro. Sometimes you need throwaway interface code that does something very specific on a very tight platform. If you want to treat a block of memory as a block of memory, use a block of memory. I have three short ints that hold 3 16-bit wide calibration values.set by user. Joshua Honig
Treating it like an array assigns each value to the sub-variable in the same order as the struct was defined. int res = eeprom_write(addr, *ptr); Externally-imposed data formats, such as interfaces to hardware devices, also often require the ability to get at pieces of a word. Here is a snippet from Second Edition of [i]The C Programming Language[/i] by Brian W. Kernighan and Dennis M. Ritchie, http://www2.cs.uregina.ca/~hilder/cs430-833/Reference%20Materials/The%20C%20Programming%20Language.pdf. I write code for very memory-constrained microcontrollers, and sometimes I have to write assembler just to fit it all in. Then in my custom Interpreter class (an instance of Interpreter is created in the Main.cpp code file and the Main() sub starts a Run() loop on that Interpreter instance) I have a 64-byte structure defined as: The Number field is essentially a string with a max character length of 53. Did you check with a simple check if that works correctly for 64 bytes? Thank you very much for writting the whole function out. Christoph has updated the log for Bringing up a new Betaflight target: STM32H725/735. Can a judge force/require laywers to sign declarations/pledges? Hi, I have a python app that i want to be able to get variables from a php page on my webserver. uint16_t value; But lets get real. I have a byte array I want to convert to a string. So you write a routine (you could do eeprom bounds checking if required etc) and assuming you arent doing more than 254 byte writes, which you probably arent on a constrained system. hth. There are at least twopossibilities to do so: Following the same reasonings as the other way round, a quite concise method can be written to achieve the desired array-wise interpretation, both the structure type S as well as the array element type E being generics. union has side effects. And you (I assume) are never going to manually change Uint64, you are just going to pass it to a function that you dont control. What is going wrong now is that in the loading you give it a pointer to a fixed ProductionItem. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This is clear to read and at least not compiler-dependant ! The content you requested has been removed. Learn how your comment data is processed. As far as I know in Visual Basicyou have to send data over a socket as a byte array. Convert object to byte array and return it from the Read implementation? That might seem like a strange concept, but lets see how that can be used to easily access different single bytes within a longer data type. Hopefully we could give you some new insights and ideas of how to arrange your variables, and some convenient alternatives to handle them. Not just another platform, Ive had terrible problems with structure alignment on Solaris, when trying use gcc to build some code that simply refused to compile correctly with Sun CC. I'd like to read in a binary file, convert it's 4 byte values into Once the struct has its own identifier, we can also add a type name to the struct itself, which lets us use it also outside the union. I have a need to turn byte arrays into various structures. Expanding on my comment; below you'll find a very simple program that compares the method I suggested with your original example. public byte deviceType;. The you dont have to worry about accidently writing to one variable while whacking another (the union way..). messageStruct.hdr3 = 7
By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use. And theyre useless if you want to combine different data types together. I'd like to create n structs based on data in the byte array. public byte versionMinor;. Even when C was first written, it was obvious that there would have to be platform-specific things that would need to be rewritten. As for the union, Im using it to cast the blob of memory you refer to as the kind of variable type that I need. The web application and the Java application are both running on the same machine. I am trying to convert byte array (read from another process memory), this byte array is a map. 2. Anyway, this was a fairly meaty and interesting article. messageStruct.msg2 = 0
#. roopse March 1, 2017, 12:35pm #10. More details: a="01110011" has been finalized. But i want to getting your code review - maybe i'll have any memory leak? With minimal changes, the method has evolved into a generic version now, which makes accessible about any structure on a bytes array. But sometimes, it doesnt matter. I almost get it, anyway, would someone help me get it? The primitive types are Boolean, Byte, SByte, Int16, UInt16, Int32, UInt32, Int64, UInt64, IntPtr, UIntPtr, Char, Double, and Single. Instead of defining your structure the traditional way, you can use [MarshalAs(UnmanagedType.ByValArray, SizeConst = n)] to define a managed type variable in order to convert a bytes array to a structure or convert a structure to a bytes array. C# / C Sharp I have a large structure, below is a simplistic version of my structure: Jan 21 '08
Just use the union knowing data isnt reliable if they call something else -> no problem, some advantage (nicer code). Dim el3 As Byte 05 C REDEFINES A PICTURE 99V99. The best answers are voted up and rise to the top, Not the answer you're looking for? Dim el1 As Byte I'd like to create n structs based on data in the byte array. (Don't forget to release the handle with GCHandle.Free.). The namespace Runtime.InteropServices has appropriate methods to deal with such situations. For Object, this obviously makes sense, as ultimately everything is an object, so there's no need in specifying such a constraint. It probably has to do with passing the value between methods but I don't know where I've gone wrong. var point = new Point (10,5); byte [] serialized = point.ToByteArray (); Point deserialized = serialized.ToStructure<Point> (); my reading of ptrtostructure is that it will work with any type, class or struct. but you cant count on it. For instance, an often seen suggestion is to use the Marshal.SizeOf method on the structure to be filled, then to allocate an appropriately dimensioned buffer in a bytes array, proceed to use one of a variety of Copy methods (Array.Copy is also mentioned frequently) to fill this buffer, obtain a pinned handle with the GCHandle.Alloc method, then use Marshal.PtrToStructure with the obtained handle on the structure type, which after casting to the structure type will contain the data. after converting above struct to byte array i passing it to cobol program, in cobol program input values are not placeing for each feild ie. Yes, performance is crucial. For performance reasons, different processors also like to align memory on 2-byte or 4-byte boundaries, which may mean that two uint8_ts might be located four bytes apart in memory. }. Still, it would be better to encapsulate it and pass an address of the structure instead, it would be much clearer and less prone to errors.. Un-Ionized? If you ever wondered what a float looks like to a CPU, just make it think its an integer. Assume the existence of a tightly packed structure like this: and a bytes array initialized as follows: The caller would then use the above method thus: Care must be taken on the interpretation of the retrieved data. Ok I was being a dolt and forgetting the length parameter on the memcpy statement that's why it I was getting a parameter error. We could also add a 2-bit wide fourth field to use the remaining space at no extra cost. The results on my machine show that the MemoryMarshal class is about 85x faster. Nice article. For example signalling between different layers of software. If there is a better way please advise. When I convert this all to ASCII and try to send it works just fine. With its simplicity, versatility, and robustness, Python Base64 string from byte array - what's the length ratio ? To ensure we end up with an unsigned 16-bit integer variable regardless of the underlying system, well be using the C standard librarys type definitions from stdint.h. 1. struct foo* tmp2 = (struct foo*)byte_array2; is bad C code because the behavior of accessing an array of char through a struct foo lvalue is not defined by the C standard. How to use http requests (Get function) to get variable value? }.
I have a huge byte array from another API that contains structs of differing sizes. 1. I'm looking To me, the primary advantage of floating point numbers is their ability to hold very very large numbers or very very small numbers, but I dont need that for most of my code. So i trying to improve that to the version 2: I have found that this version getting very good performance.. HOW CAN I CREATE AN AI with an .executable file that would suck all files in the folder and on my computer, How do I view Redshift db tables in Alteryx, Mastering Python: A Versatile Programming Language for All. Dim el2 As Int16 Passing a pointer to the struct to get lots of info where its needed is a fine and dandy trick. The classical C++ mechanism to create a type alias is typedef. Can someone explain me this phenomenon with QByteArray(struct,memcpy)? Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site. So if you ever end up analyzing some raw data dump or binary blob and come across a floating point value, now you know how to use a union to find out what number it represents. Luckily, C provides us with proper alternatives out of the box. convert a IntPtr to a byte to be able to add a meetingBlob data to the by: Mario M. Mueller |
Many programmers avoid them and stick with doing explicit bitwise operations so that they know their code will always work. int nVal2; this Exemple in Cobol : Prabhu. Method 1: Using BitConverter. This thread has been closed and replies have been disabled. This member has not yet provided a Biography. So if a struct sensor_data variable starts at memory address 0x1000, the temperature field will be located at 0x1000, the humidity field at 0x1010, and the brightness field at address 0x1020. Though both mean the the same thing. This seems like a good way to make nightmares for anyone trying to port your code to another platform some day. Its always is clear from inspection how I am using the memory and I dont have typecasts sprinkled all over the place. It would be nice, if a constraint existed also to accept only arrays, but MS laconically states: The following types may not be used as constraints: Object, Array, or ValueType. Anyone who says that code should be its own documentation is a moron. I am trying to hook up a CPU which I designed using SystemC to I/O pins on an FPGA. You might want to experiment a bit and try running a similar test with a larger struct; maybe your method is faster for the specific problem that you're trying to solve. How do I Derive a Mathematical Formula to calculate the number of eggs stacked on a crate? If you find that you forgot something, just add it to your struct definition and it automatically is passed along for the ride without having to modify your function definition (i.e. How does TeX know whether to eat this space if its catcode is about to change? Following the formats definition, we can construct the initial floating point number 65.65625 back from it. This works Blockchain technology has emerged as a transformative force in the business world, offering unprecedented opportunities for innovation and Am having a bit of a time with URL Rewrite. uint32_t size; Most computers and microcontrollers are little-endian, but watch out for Motorola 68k and AVR32 architectures which are big-endian. Now you can swap between single byte/char access and formated data access. Your comment about code being crap for using unions and structs is just plain wrong. Once I've found these two bytes Hi, The file size is held in a short (2 byte If you have any problems with the registration process or your account login, please contact us. ), youre going to have pointers. You have the following line in both of these functions: The sizeof(data) will always be 4 since that is the size of a pointer on this 32-bit architecture. }; int eeprom_write(size_t addr, uint8_t byte); int save(const struct config_t* const cfg) { Simply pass a struct or union (or better yet a pointer to one, since structs pass by being copied onto the stack otherwise) to your function. Need to convert an arbitrary byte-pair to an int. Last Visit: 31-Dec-99 18:00 Last Update: 5-Jun-23 3:42, Recommend changing term "primitive datatype" to "blittable datatype". When storage space is at a premium, it may be necessary to pack several objects into a single machine word; one common use is a set of single-bit flags in applications like compiler symbol tables. Thanks for contributing an answer to Code Review Stack Exchange! (Comment Policy). That's why we've created a SaaS Introduction: The size of the union itself will be equal to the biggest fields size, so with a 32-bit and a 8-bit integer, the union will be 4 bytes in size. (1) arbitrary (aligned) structure records (possibly containing dynamically-sized strings and in general arrays of (not only blittable) datatypes) and. At the moment, I'm using this: How Blockchain technology has emerged as a transformative force in the business world, offering unprecedented opportunities for innovation and . Thank you Hackaday! http://stackoverflow.com/questions/3278827/how-to-convert-a-structure-to-a-byte-array-in-c. Is the other process you are reading from an unmanaged process? I read it in the same order. At another point the numeric values worked if I saved them twice or more, but then the item number was always truncated. return sz; Lets consider a real world example involving the ATmega328s analog-to-digital converter. like transporting a struct from an mcu to a computer did require bit shifting at one end to decode the data correctly. All forums and questions are now archived. Most C/C++ people will also avoid using direct in-line assembly as well, and when necessary wrap an abstraction with a meaningful comment explaining why it was done. Show me the way. Whoops, you are right, I had a hex number printed there in an earlier draft and forgot to properly adjust it. ByVal d as dat gives an error so I replaced that with ByVal dAsMsgStruct-which is mystuct type. I will provide such as well, as soon as the main goal to convert between. Ill leave it for you to decide which option is clearer to read and easier to maintain. The above method now allows any array of primitive datatypes to be interpreted as any structure record, but it's still not flawless. As you can see, the struct has neither a type name nor has the field itself a name, which lets us access the fields inside the struct as if they were part of the union itself. If you have it like that you should do that part with memcopy.". I need a fast method for converting an int array to a byte array. 1) write code that some other idiot is going to have to maintain or change in the future. I have the following delphi structure for a binary file. Range-checking at the start of your API will spend many fewer cycles than the generated machine code and bus cycles to manipulate less-than-register-sized values. A common solution to perform a binary copy of an array using the std::memcpy function. Fortunately, the constraint can easily be achieved by changing the method's signature to accept arrays only instead of specifying a generic: Now only arrays can be fed to the method, returning the result to any structure record. The C programming language is probably not the language you should be using. Make convenient scratch-pad variables without having to declare them within each function. To stick with the sensor data example, lets assume each sensor value is read by an analog-to-digital converter (ADC) with 10-bit resolution. To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page. mit41301 liked RGB LED control with Op Amp and ADXL335. That means only the first 4 bytes of your structure are actually being read/written from/to FLASH. You do not have the correct permissions to perform this operation. struct variant_t { Most .NET-conforming signature, but building and returning the array is very expensive. public byte appId;. I want structs like this: public struct SItuPollResponse . The Field Offset attribute accept an argument for how many bytes from the start of the structure to offset to that field. How would I make it HOW CAN I CREATE AN AI with an .executable file that would suck all files in the folder and on my computerHOW CAN I CREATE AN AI with an .executable Hi, So I have methods which read/write a char* to flash: These are defined in a custom FRamIO wrapper for a FRAM (basically a fast EEPROM). QDataStream >>QByteArray [was QByteArray resize not working?! Dim bytes() As Byte = ASCII.GetBytes(messageStruct)
signalId, senderId, timestamp) and the rest completely different. Unions would be the simplest solution for interpreting arrays as structures, and structures as arrays, making conversions unneeded. string? in my source I receive a byte array (for eg: 0xED, 0xFF, 0x01, 0x3D). bornach has updated details to Rainbow LED Effects using PWM Generated by OpAmps. Using std::memcpy. Should I trust my own thoughts when studying philosophy? So I've corrected those two routines. I then can write first char from array to first EEPROM address, then second to second, etc. If you want to use a type variable, use one. (Just writing 1-64 for example). Assume it's interesting and varied, and probably something to do with programming. char szText[10]; struct t_any_data Data; Thats why the union keyword exists. ], Qt Centre - The Ultimate Qt Community site, If this is your first visit, be sure to Convert Object/Struct to byte[] without serialization. In a sense, unions provide a shortcut to data type conversions, while at the same time making sure the data itself is used in a way that makes sense and is valid in its context, with the compiler keeping you honest. Most platforms have a quite rigid ABI specification, so the compiler doesnt have much freedom on how to lay it out. messageStruct.msg1 = IglobalKeyPress (which is an integer) messageStruct.msg2 = 0. messageStruct.msg3 = 0. http://www.functionx.com/cpp/articles/serialization.htm. Thus, care must be taken in interpreting the result, especially in little-endian systems like Intel's. by: =?Utf-8?B?Vmlua2k=?= |
As a non C programmer this looks hideous. But yeah, the C standard itself makes no guarantees here. For those using C# you can achieve a union using explicit struct layout. IntPtrptr=Marshal.AllocHGlobal(Length). I really am thankful industry decided to embrace an unofficial standard compiler after 35 years of pain-in-class compilers. I also tried to define it as a struct: Anyway, I am having troubles with reading it. Following is the code I have written so far. The results on my machine show that the MemoryMarshal class is about 85x faster. it starts at &mystruct and has the length of sizeof (mystruct_type) bytes. I thought I should be able to simply assign the struct instance to the char array but couldn't get that to work. On a proper CPU, a functions local variable allocation is always ideal, because exactly the right amount of space is allocated as its needed, per function and only the required space thats needed for live variables in the entire program or thread is currently occupied. I apologize for the convolution of the code in question but I have often found that I can make a simple example work just fine and the problems only occur when I try to structure my code into a domain model and start passing parameters between methods that's always when things get wonky on me so that's why I wanted to keep the context of the chain of method calls that I need to use. Storing the results in 16-bit integers will therefore waste 6 bits for each value, which is more than one third. struct sensor_data data; data.temperature = 123; data.humidity = 456; data.brightness = 789 . A few comments: A structure is a byte array. Let's declare a variable of this new type and assign values to each of the struct 's field. Both will output 0x42835000 which wont tell us much without thoroughly studying the binary32 format, which is a combination of a sign, exponent, and fraction value with a standardized bit width. If something is horrendously big; you might use a bit in flags to indicate that size is measured in 16-bit words or 32-bit long words. I'd like to create n structs based on data in the byte array. Still I think you have to split it up, then you can find out when it goes wrong exactly. A union essentially gives one memory location different names and correspondingly different sizes. The union approach will just lead to bugs, side effects, and hard to maintain code. Making statements based on opinion; back them up with references or personal experience. Before proceeding with incorporating the method, it might be a good idea to check out what could go wrong. a= "00001010" I have structure as below in C# which is equal to Cobol Copy book structue, Oct 17 '10
Note that the data type sizes dont need to match, so its no problem to have a union with, for example, a 32-bit and a single 8-bit integer, the 8-bit value is simply truncated if needed. Everyones needs are a little different. And this is pretty much all there is to know about bitfields. uint8_t byte[8]; I'm too spoiled by intellisense for this web IDE lol. function float2rawInt() in java, but I don't know the internal Instead of
I think if you intend to use unsafe code in c#,you can use the structure pointer directly. My objective is to convert obj to byte array and read it through the implementation of Read trait. ClientSocket.Send (bytes) I did an ethereal snoop on the packet accross the network and the data isn't being sent. Note that accessing the struct fields anonymously will only work as long as there are no name conflicts. Taking the structure between architectures also exposes you to byte order issues even if the compilers agree on exactly how big data elements are and padding is done. I get an error when I execute the code this way. If youre writing in some other language and you need to unpack structures that are passed back and forth from C code, you will most certainly have to learn how to do this stuff. int64_t int; nah, too complex. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Alternatively, the struct can be initialized directly while declaring it. I have been struggling to find out how to use a variable as my location in my header redirect function. The encoding/gob package of the Go standard library provides you an easy way to serialize your struct to bytes. Sending the data in binary would require 4 bytes each, and NO loss of accuracy. public byte msgType;. In doing so, iHandle.AddrOfPinnedObject will yield 0, and Marshal.PtrToStructure with 0 will throw the exception System.NullReferenceException. I need some help in converting a byte array to pdf. My python app is on my computer. Convert an integer array to a byte array. What this means in practice is easily shown once we assign values to all the fields like we did in the struct example earlier. last post by: Hello Everyone, If i understand good - it seems that according to the Benchmark results,the first method is faster than the second method. while (sz) { The contents in the following table are shown in hex. Notice how the fields in the designated initializers are not in their original order, and we could even omit individual fields and leave them simply uninitialized. Pro or contra? (given it does need error checking, better to have it return a true/false even at this stage). This member has not yet provided a Biography. The bitfield is a special-case struct that lets us split up a portion of an integer into its own variable of arbitrary bit length. Ask Hackaday: Whats Your Tactical Tool Threshold?
What is the command to get the wifi name of a BSSID device in Kali Linux? By disabling cookies, some features of the site will not work. Does somebody know what's the length's ratio in we convert byte to base64 And markedly, on a bytes array only, so the method still is of somewhat limited use: what if the array is to represent Unicode characters, or 3-dimensional locations in double precision? Let us know if you can think of other ways to make use of all this, and in what peculiar ways you have used or come across unions before. If there are duplicate field names, the struct itself will require a field name. So things that reduce the chance of errors is good! std::array< byte, sizeof(T) > is a wee bit easier on the eye than std::array< unsigned char, sizeof(T) >. By continuing to use our site, you consent to our cookies. They are good! The simplest way is by writing the data byte by byte to a respectively incrementing memory address on the PLC - it's a simple task for me to write the PLC code to reconvert to a struct on the other side. Lets say we want to store three 16-bit integers representing the values of a temperature, humidity, and light sensor. Frame.Bytes[0] = 7; Access nVal1, Byte 0, overwrites with 7. Each is 4 characters, with a huge loss of accuracy. Writing FP code is trivial in most cases (with non-IEEE floats) and take little space. It is that simple. In this sample, I have used only one class. And this is indeed possible, requiring just minimal changes once again. Using bitfields will let us use a single 32-bit integer and split it up in three 10-bit variables instead, leaving only 2 bits unused altogether. Unlike the struct example, the value printed here wont be the assigned value 123, but 789 instead. struct { Little-endian architectures will interpret the array index 1 as the integers second least significant byte 0x56, while big-endian architectures will interpret it as the integers second most significant byte 0x34. typedef unsigned char byte ; i.e. The other fields are simple numeric values as they appear. Ive only been program in C for a bit over 40 years (I still have an original copy of K&R on the shelf) :-), and Id generally say that if are using the union feature you either a) dont know what you are doing b) your program is crap, or c) both. Share. Of course, it doesnt require a union to combine those two register values, we could also just use bitwise shifting and an OR operation: Truth be told, there is actually nothing unique about unions. Sorted by: 1. If speed and memory efficiency are secondary concerns and portability is the primary concern, then go use whatever high level language you want. Ill declare a global array of unions, each element of which can be a single uint32_t, two uint16_t variables, or four uint8_t variables (I generally avoid floating point in my embedded code). \o/ Why? Quite similar to the union option tbh, with both some small pros and cons. Copying the data isn't working either - I typically get corrupted results. I am quite sure that the read and write to the memory is correct. C# / C Sharp. To start a new conversation I'm pretty good in managed code, but there's still a lot about basic unmanaged code that eludes me it maybe that the issue I'm seeing stems from some other underlying problem; but I do have a lot of seemingly working functionality so I suspect the issue lies somewhere near the symptom. Thanks for the help thus far everyone, but I'm still not getting it @Adam: Ah of course at one point I was trying to pass an actual character array and then the count was accurate, when I changed to the pointer I failed to consider the change to the sizeof result. Hi Reed, what you are looking for is serialization of the objects, where the struct is in fact a C++ object. The floating point library is just too big! Almost every modern mcu I have used will have a specific subset of special macros to handle platform specific eccentricities. Thanks & Regards Prakash Prabhu. Two options I currently see: Reading/writing from/to your memory goes wrong. MTG: Who is responsible for applying triggered ability effects, and what is the limit in time to claim that effect? If someone could help me understand how to properly pass the struct instances around and serialize them to/from the flash, I would be greatly appreciative. Tight (and readable) code is at the top of my list. A possible function to convert a byte array to a record of a hypothetical structure STarget without copying anything would be: While this does fulfill the request to give access to the bytes array via a structure record's members, it is quite a specific solution targeted at just the structure type STarget. . Lets declare a variable of this new type and assign values to each of the structs field. 05 B REDEFINES A PICTURE 9V999. Advantage of AntDB: hyper-convergence + streaming processing engine public int pollNumber; to be converted to an array of bytes so I can send it across the serial port, done by a method that takes a byte[] and a count. This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL), General News Suggestion Question Bug Answer Joke Praise Rant Admin. On an 8-bit PIC, the compiler attempts to do this by creating a statically allocated stack, but variables from different functions at the same call level will occupy the same RAM addresses: they are part of a union. This concludes our expedition into structs and unions. public static byte Int2ByteArray(int array) by: Dmitri Shvetsov |
I really just need to be able to convert a struct into a byte array, if I . uint64_t uint; I have a binary file containing 3 byte float values (big endian). I suspected something like this was necessary but have not yet found the correct way to write the memcpy statement. Use MathJax to format equations. Well, here is a result of reading it: union adc_data { Lets have another look at the previous byte-extraction example and see what other options we have to get a single byte out of an integer. I, too, have 40 yrs experience, with most of that dealing with hardware manipulation (CPU, PCI, etc.). uint16_t cal_x; Hello Reed, in your above example the FRamIO::WriteByte and FRamIO::ReadByte methods calculate the number of bytes to write/read incorrectly. messageStruct.hdr4 = 1
In the overall architecture, a new "hyper-convergence" concept was Hi there. (please correct me if I am wrong I am new to VB). If someone could please baby-step me through the struct-to-byte array conversion process I would be very grateful. . Enlighten me. I'm trying to size a jpeg file. It can be used to convert a string to a byte array along with the std::string::data function, which returns a pointer to an array containing the C-string representation of the string object. Were sorry. Floating point is useful for some data. Thank you so much everyone! Any words on them? thread 'main' panicked at 'destination and source slices have different lengths', /Users/harsh/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/slice/mod.rs:2554:9. I want to save them to internal EEPROM, but I can only write 8 bits at a time, and I have to read them in the same order upon reboot. So please any one can help me by Hello, One thing (already mentioned here) that from time to time bites me its how structs are packed. Minimum use of memory and the type cast is always correct. 1. Here is my function to convert bytes into struct: I am using pointers, since performance is very important in my case - game map will be read at least 100 times per second. I have a huge byte array from another API that contains structs of differing How to make the pixel values of the DEM correspond to the actual heights? Asking for help, clarification, or responding to other answers. And even then, dereferencing a pointer is clearly changing something in memory.. size_t addr = 0x12340000; /* EEPROM address */ Following is the code I have written so far. Please, Wise One, enlighten me, how I should correctly solve a following problem: Im writing for 8-bit micro so memory is accessed in single bytes. Now, applying the same terminology to the union declaration, we basically tell that whatever is located at the unions memory address is either one 32-bit or four 8-bit values, so just like we can do with the cast except, with a union, we will be very explicit which one of those two types it will be when we access the value. o.O I mean, how does converting a struct into a string inside a file and then reading that file to QByteArray is anyway reasonable? For completeness, the same data is also extracted with bitwise operations as a non-union alternative. Re: please show the missing C# code for: Fast Conversions between Structures and Arrays. You change that pointer in your function to point at new data, but that doesn't change the value you get outside the function, which is why you get that error. Mark the struct with a StructLayout attribute with the parameter LayoutKind.Explicit and then apply FieldOffset attributes to each field. Also, this method is very flexible. Unless you live by declaring everything statically in one place where its all globally accessible (ugh! Taking a closer look at the pointer casts, we basically tell that whatever is located in the memory address of the 32-bit value, is in fact a collection of 8-bit values. messageStruct.msg3 = 0
Well, here is a result of reading it: Its not what I want to get, I want to get an array of tiles. And a third one, what I generally use is something like: So you just make a pointer to a char, and then you give it as value the pointer to your struct, casted to char pointer. I am doing the curl get request from my web Hello Folks, Assume it's interesting and varied, and probably something to do with programming. I have found that when i calling to the first version a lot of times in a second - i getting poor performance. The array needs to be instantiated appropriately by the caller. Perhaps, but it does depend on whether youre writing on a blackboard or stuffing your face :). Sound ok? return res; =D it does look fast, clear and easy for me. or read the latest updates go to For debugging however it is handy to try to keep it as simple as possible. in order to display the array's elements on the console (again with leading zeroes for illustration purposes only): This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL), General News Suggestion Question Bug Answer Joke Praise Rant Admin. Join Bytes to post your question to a community of 472,354 software developers and data experts. vs just calling BinaryReader/BinaryWriter et al, to shuffle between byte[] and managed struct? All rights reserved. last post by: Hi All, Youll be auto redirected in 1 second. I am trying to implement std::io::Read trait for a struct. Finally, as specified they only work with int sized-items. You could say that unions are to pointers what enums are to a bunch of preprocessor constants. As MsgStruct
In whichever way you are using them, you could achieve the same with either bitwise operations or pointer casts. In this article, two fast-performing methods are presented to interpret arbitrary arrays of primitive datatypes as structure records, and vice-versa. for(uint8_t i=0;i
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