Problem converting GUID strings to hexadecimal in C [DUVIDA]

backtrack5R1 · 05-16-2024, 06:28 PM

I am facing difficulties in implementing a function in C to convert GUID strings into hexadecimal representations. The function I am using is the following:

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>

#define MAX_GUID_STRING_LENGTH 39

typedef struct {
  unsigned int  data1;
  unsigned short data2;
  unsigned short data3;
  unsigned char  data4[8];
} GUID;

void stringToHexGuid(const char *input, char *output)
{
 unsigned int dword1, dword2, dword3;
 unsigned int byte1, byte2, byte3, byte4, byte5, byte6, byte7, byte8, byte9, byte10, byte11;

 sscanf(input, "{%8X-%4X-%4X-%2X%2X-%2X%2X%2X%2X%2X%2X}", &dword1, &dword2, &dword3,
        &byte1, &byte2, &byte3, &byte4, &byte5, &byte6, &byte7, &byte8);

 byte9 = (byte2 << 8) + byte3;
 byte10 = (byte4 << 8) + byte5;
 byte11 = (byte6 << 8) + byte7;

 snprintf(output, 100, "0x%08X, 0x%04X, 0x%04X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X",
          dword1, dword2, dword3, byte9, byte10, byte7, byte8, byte9, byte10, byte11, byte8);
}

This function receives the inputs:

Code:

7FFEC5C92D0049B789413EA10A5586B7
7FFEC5C9-2D00-49B7-8941-3EA10A5586B7
{7FFEC5C9-2D00-49B7-8941-3EA10A5586B7}

and should convert the string to an exadecimal GUID structure as well as the original GUID, reaching the following result:

Code:

{0x7FFEC5C9, 0x2D00, 0x49B7, 0x89, 0x41, 0x3E, 0xA1, 0x0A, 0x55, 0x86, 0xB7}

but the function does not correctly convert to hexadecimal and produces the following results:

Code:

//origen: {0x7FFEC5C9, 0x2D00, 0x49B7, 0x89, 0x41, 0x3E, 0xA1, 0x0A, 0x55, 0x86, 0xB7}

//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x413E, 0xA10A, 0x86, 0xB7, 0x413E, 0xA10A, 0x5586, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x8D1, 0x7E1, 0x86, 0xB7, 0x8D1, 0x7E1, 0x2D5, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x8D1, 0x3E1, 0x86, 0xB7, 0x8D1, 0x3E1, 0xF5, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x89, 0x3E, 0x86, 0xB7, 0x89, 0x3E, 0x0A, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x41, 0x3E, 0x86, 0xB7, 0x41, 0x3E, 0xA1, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x41, 0x3E, 0x86, 0xB7, 0x41, 0x3E, 0xA1, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x89, 0x41, 0x86, 0xB7, 0x89, 0x41, 0x3E, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x8941, 0xA155, 0x86, 0xB7, 0x8941, 0xA155, 0xB73E, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x893E, 0x410A, 0x86, 0xB7, 0x893E, 0x410A, 0xA155, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x413E, 0xA10A, 0x86, 0xB7, 0x413E, 0xA10A, 0x5586, 0xB7
//error: 0x7FFEC5C9, 0x2D00, 0x49B7, 0x8D1, 0x481, 0x86, 0xB7, 0x8D1, 0x481, 0xF5, 0xB7

How do I convert the function to hexadecimal as it was in the original GUID?

NevemTeve · 05-17-2024, 02:44 AM

First remove every syntactical character ({-}) then check the length (32) and the characters one-by-one (0-9a-fA-F), and finally do the conversion, the output should be `uint8_t[16]` or similar.

GazL · 05-17-2024, 03:20 AM

I really would have expected the placement of the hyphen delimiters to match the layout/size of the members of the GUID struct, but apparently not. Microsoft are weird!

ntubski · 05-17-2024, 07:28 AM

Quote:

Originally Posted by backtrack5R1

Code:

 byte9 = (byte2 << 8) + byte3;
 byte10 = (byte4 << 8) + byte5;
 byte11 = (byte6 << 8) + byte7;

 snprintf(output, 100, "0x%08X, 0x%04X, 0x%04X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X",
          dword1, dword2, dword3, byte9, byte10, byte7, byte8, byte9, byte10, byte11, byte8);
}

I don't understand why you are splitting up and then combining bytes like that, but it looks like you skipped byte1 and are using byte7, byte9, byte10, byte11, and byte8 twice.