将Packed C结构转换为Go结构体时出现问题，通过cgo。

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英文:

Problem in converting Packed C structs to go structure by cgo

问题

当我们使用#pragma pack (push, 1)对C结构进行打包，并通过cgo转换为Go结构时，转换后的Go结构中有一些字段丢失。

我正在使用的Go版本是：1.16.6 Windows/386

例如，我的C结构如下所示：

  1. #pragma pack (push, 1)
  2. typedef struct _sample_struct
  3. {
  4. 	USHORT                   usNo;
  5. 	DWORD                    ft;
  6. 	DWORD                    fit;
  7. 	CHAR                     cID[5];
  8. 	CHAR                     cCID[3];
  9. 	ULONG                    ulVal;
  10. 	ULONG                    ulIn;
  11. 	ULONG                    ulCnt;
  12. 	ULONG                    ulMax;
  13. 	USHORT                   usStat;
  14. 	BOOL                     bAlk;
  15. 	LPSTRUCT2                lpNNL;
  16. 	USHORT                   usNPCU;
  17. 	LPSTRUCT4 *              lppP;
  18. 	LPSTR                    lpBuff;
  19. 	LPUSHORT                 lpusIDS;
  20. 	WORD                     usType;
  21. 	LPSTR                    lpszCUName;
  22. 	ULONG                    ulICnt;
  23. 	ULONG                    ulDCnt;
  24. 	ULONG                    ulPCnt;
  25. 	ULONG                    ulRCnt;
  26. 	ULONG                    ulRJCnt;
  27. 	ULONG                    ulMin;
  28. } SAMPLESTRUCT, *LPSAMPLESTRUCT;
  29. #pragma pack (pop)

转换为Go后，结构如下所示：

  1. type _Ctype_struct__sample_struct struct {
  2. 	usNo		_Ctype_USHORT
  3. 	_		[8]byte
  4. 	cID		[5]_Ctype_CHAR
  5. 	cCID		[3]_Ctype_CHAR
  6. 	_		[16]byte
  7. 	usStat		_Ctype_USHORT
  8. 	bAlk		_Ctype_BOOL
  9. 	lpNNL		_Ctype_LPSTRUCT2
  10. 	usNPCU		_Ctype_USHORT
  11. 	_		[12]byte
  12. 	usType		_Ctype_WORD
  13. 	lpszCUName	_Ctype_LPSTR
  14. 	ulICnt		_Ctype_ULONG
  15. 	ulDCnt		_Ctype_ULONG
  16. 	ulPCnt		_Ctype_ULONG
  17. 	ulRCnt		_Ctype_ULONG
  18. 	ulRJCnt		_Ctype_ULONG
  19. 	ulMin		_Ctype_ULONG
  20. }

正如我们所看到的，一些字段没有正确转换；相反，它们有“_”。

如果没有#pragma pack行，转换是正确的；然而，我需要进行打包，因为我使用的库对发送到我们应用程序的结构要求进行打包。

有没有解决这个问题的方法？

英文:

When we use #pragma pack (push, 1) to pack the C structure and convert to go structure by cgo, some of the fields are missing in the converted Go structure.

I am using Go version: 1.16.6 Windows/386

For example, my C struct is like this:

  1. #pragma pack (push, 1)
  2. typedef struct _sample_struct
  3. {
  4. 	USHORT                   usNo;
  5. 	DWORD                    ft;
  6. 	DWORD                    fit;
  7. 	CHAR                     cID[5];
  8. 	CHAR                     cCID[3];
  9. 	ULONG                    ulVal;
  10. 	ULONG                    ulIn;
  11. 	ULONG                    ulCnt;
  12. 	ULONG                    ulMax;
  13. 	USHORT                   usStat;
  14. 	BOOL                     bAlk;
  15. 	LPSTRUCT2                lpNNL;
  16. 	USHORT                   usNPCU;
  17. 	LPSTRUCT4 *              lppP;
  18. 	LPSTR                    lpBuff;
  19. 	LPUSHORT                 lpusIDS;
  20. 	WORD                     usType;
  21. 	LPSTR                    lpszCUName;
  22. 	ULONG                    ulICnt;
  23. 	ULONG                    ulDCnt;
  24. 	ULONG                    ulPCnt;
  25. 	ULONG                    ulRCnt;
  26. 	ULONG                    ulRJCnt;
  27. 	ULONG                    ulMin;
  28. } SAMPLESTRUCT, *LPSAMPLESTRUCT;
  29. #pragma pack (pop)

Converted to Go, the structure looks like below:

  1. type _Ctype_struct__sample_struct struct {
  2. 	usNo		_Ctype_USHORT
  3. 	_		[8]byte
  4. 	cID		[5]_Ctype_CHAR
  5. 	cCID		[3]_Ctype_CHAR
  6. 	_		[16]byte
  7. 	usStat		_Ctype_USHORT
  8. 	bAlk		_Ctype_BOOL
  9. 	lpNNL		_Ctype_LPSTRUCT2
  10. 	usNPCU		_Ctype_USHORT
  11. 	_		[12]byte
  12. 	usType		_Ctype_WORD
  13. 	lpszCUName	_Ctype_LPSTR
  14. 	ulICnt		_Ctype_ULONG
  15. 	ulDCnt		_Ctype_ULONG
  16. 	ulPCnt		_Ctype_ULONG
  17. 	ulRCnt		_Ctype_ULONG
  18. 	ulRJCnt		_Ctype_ULONG
  19. 	ulMin		_Ctype_ULONG
  20. }

As we can see, some of the fields are not converted properly; instead, it has "_".**

Conversion is correct without the #pragma pack lines; however, I need packing in place because the library that I use imposes packing for the structures that are sent to our application.

Is there any solution to this problem?

答案1

得分: 1

我实际上在这个问题上写了一篇完整的博客文章：https://medium.com/@liamkelly17/working-with-packed-c-structs-in-cgo-224a0a3b708b

简要说明如下：

  • 查看Go的GitHub维基页面，在cgo部分他们明确提到cgo不会对结构体进行打包
  • 你可以很容易地自己打包结构体，类似于将结构体编码为JSON然后发送。通过使用binary包，你可以迭代结构体成员并将它们放入[]byte中。然后可以将[]byte作为打包的结构体传递给C函数（从C函数接收打包的结构体则相反操作）。
英文:

I actually wrote a whole blog post on this: https://medium.com/@liamkelly17/working-with-packed-c-structs-in-cgo-224a0a3b708b

The quick notes are:

  • Look at the Go wiki page on GitHub, in the cgo section they explicitly mention cgo will not pack structs
  • You can very easily pack the structs yourself in a similar to encoding a struct to JSON before sending it. By using the binary package you can iterate through struct members and place them into a []byte. The []byte can then be passed as a packed struct to C functions. (do the opposite to receive packed structs from c functions)

huangapple
  • 本文由 发表于 2022年7月5日 16:28:36
  • 转载请务必保留本文链接：https://go.coder-hub.com/72866267.html
  • c
  • cgo
  • go
  • pragma-pack
  • struct
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