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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. typedef unsigned char   u_char;
  5. typedef char CCHAR; 
  6. typedef int16_t WCHAR;
  7. typedef uint32_t ULONG;
  8. typedef uint32_t DWORD;
  9. typedef uint64_t LARGE_INTEGER;
  10.  
  11. #pragma pack(1)
  12.  
  13. typedef struct smb2_FileBothDirectoryInformation {
  14. 	ULONG         NextEntryOffset;
  15. 	ULONG         FileIndex;
  16. 	LARGE_INTEGER CreationTime;
  17. 	LARGE_INTEGER LastAccessTime;
  18. 	LARGE_INTEGER LastWriteTime;
  19. 	LARGE_INTEGER ChangeTime;
  20. 	LARGE_INTEGER EndOfFile;
  21. 	LARGE_INTEGER AllocationSize;
  22. 	ULONG         FileAttributes;
  23. 	ULONG         FileNameLength;
  24. 	ULONG         EaSize;
  25. 	CCHAR         ShortNameLength;
  26. 	CCHAR         Reserved;
  27. 	WCHAR         ShortName[12];
  28. 	LARGE_INTEGER FileId; // Missing in [MS-FSCC]: File System Control Codes - 2.4.8 FileBothDirectoryInformation
  29. 	u_char         Reserved2[2]; // Missing in [MS-FSCC]: File System Control Codes - 2.4.8 FileBothDirectoryInformation
  30. 	WCHAR         FileName[1];
  31. } smb2_FileBothDirectoryInformation_t;
  32.  
  33. typedef struct {
  34. 	uint16_t StructureSize;
  35. 	uint16_t OutputBufferOffset;
  36. 	uint32_t OutputBufferLength;
  37. 	u_char Buffer[1];
  38. } smb2_query_directory_response_t;
  39. #pragma pack()
  40.  
  41. //https://stackoverflow.com/questions/15934111/portable-and-safe-way-to-add-byte-offset-to-any-pointer
  42. template <typename T> inline void addOffset(std::ptrdiff_t offset, T *&ptr) {
  43. 	if (!ptr) return;
  44. 	ptr = (T*)((const unsigned char*)ptr + offset);
  45. }
  46. template <typename T> inline T* offset(std::ptrdiff_t offset, T *ptr) {
  47. 	return (T*)((const unsigned char*)ptr + offset);
  48. }
  49. //SomeType* ptr; int offset = 12345; offset_ptr(offset, ptr);
  50. template <typename T> inline void offset_ptr(std::ptrdiff_t byte_offset, const T* &ref_ptr) {
  51. 	ref_ptr = (T*)((const unsigned char*)ref_ptr + byte_offset);
  52. }
  53.  
  54. //If you use this marco like `typedef struct {} SomeType; SomeType* ptr; OFFSET_PTR(16, ptr);`
  55. //IDE error: expression must be a modifiable value. Compile: error C2106: '=': left operand must be l-value. 
  56. #define OFFSET_PTR(byte_offset, ref_ptr) ((const unsigned char*)ref_ptr = (const unsigned char*)ref_ptr + byte_offset)
  57.  
  58. char packet_bytes[9] = {0};
  59.  
  60. int main() {
  61. 	printf("(int)sizeof(smb2_query_directory_response_t) = %d\n", (int)sizeof(smb2_query_directory_response_t));
  62. 	printf("(int)sizeof(smb2_FileBothDirectoryInformation_t) = %d\n", (int)sizeof(smb2_FileBothDirectoryInformation_t));
  63.  
  64. 	const smb2_query_directory_response_t*  pQueryDirInfoRsp = (smb2_query_directory_response_t*)packet_bytes;
  65. 	const smb2_FileBothDirectoryInformation_t *pFileBothDirInfo = pQueryDirInfoRsp->OutputBufferLength ? reinterpret_cast<const smb2_FileBothDirectoryInformation_t*>(pQueryDirInfoRsp->Buffer) : NULL;
  66. 	while (pFileBothDirInfo)
  67. 	{
  68. 		// ideone runs on linux with a compiler who consider wchar_t 4 bytes?
  69. 		// https://stackoverflow.com/questions/16944750/c-unicode-characters-printing
  70. 		//wprintf(L"%.*s|%.*s\n", pFileBothDirInfo->FileNameLength/2, pFileBothDirInfo->FileName, pFileBothDirInfo->ShortNameLength/2, pFileBothDirInfo->ShortName);
  71. 		if (pFileBothDirInfo->NextEntryOffset)
  72. 		{
  73. 			offset_ptr(pFileBothDirInfo->NextEntryOffset, pFileBothDirInfo);
  74.  
  75. 			const unsigned char *ptrTemp;
  76. 			ptrTemp = ((const unsigned char*)pFileBothDirInfo + 10);
  77. 			//be equivalent to 
  78. 			//((const unsigned char*)pFileBothDirInfo) = ( (const unsigned char*)pFileBothDirInfo + 10 );
  79. 			OFFSET_PTR(pFileBothDirInfo->NextEntryOffset, pFileBothDirInfo);
  80. 			printf("ptrTemp = %p", ptrTemp);
  81. 		} 
  82. 		else
  83. 		{
  84. 			break;
  85. 		}
  86. 	}
  87. 	return 0;
  88. }
Compilation error #stdin compilation error #stdout 0s 15232KB
comments (?)
stdin
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Standard input is empty
compilation info 
prog.cpp: In function ‘int main()’:
prog.cpp:79:33: error: lvalue required as left operand of assignment
    OFFSET_PTR(pFileBothDirInfo->NextEntryOffset, pFileBothDirInfo);
                                 ^
prog.cpp:56:107: note: in definition of macro ‘OFFSET_PTR’
 #define OFFSET_PTR(byte_offset, ref_ptr) ((const unsigned char*)ref_ptr = (const unsigned char*)ref_ptr + byte_offset)
                                                                                                           ^~~~~~~~~~~
stdout
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Standard output is empty
https://ideone.com/Fm6EZ1
[Why (const unsigned char*)ptr is not regarded as a lvalue as left operand of assignment](https://stackoverflow.com/questions/56426040/why-const-char-ptr-is-not-regarded-as-a-lvalue)
language:
C++ (gcc 8.3)
created:
4 years ago
visibility:
secret

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