C：将收到的Winsock数据包保存为十六进制文件

Question

I need to do what most packet monitoring programs do (Wireshark, tcpdump, etc.). When data is received through Winsock, I just need to convert the packet to a hex representation and save it to file.

The data is just a simple char array.

I've tried lots of things like sprintf but with no luck. I also don't want to use itoa since it's not standard C from what I've learned.

Example:

If the packet contains "test", then it should be dumped to file as "74 65 73 74".

I can do all of the file handling stuff, and the Winsock code is working, I guess I just need to write a function to convert a char array to a hex representation, and I can't seem to get it.

Answer 1

Perhaps you should show what you have tried since printf() and its variants is by far the simplest solution.

int emit_hex( FILE* file, const char* data, size_t len )
{
    int length = 0 ;
    size_t i ;

    for( i = 0; i < len; i++ )
    {
        length += fprintf( file, "%2.2X", (unsigned)pkt[i] ) ;
        if( i < len - 1)
        {
            length += fprintf( " " ) ;
        }
    }

    return length ;
}

Answer 2

slightly more advanced function:

#include <stdio.h>
#include <string.h>
#include <error.h>

void dump(FILE* pFile, const char* szData, unsigned long ulSize)
{
  const char* pBuff = szData;
  unsigned long i = 0;
  unsigned long j = 0;

  for(i = 0; i < ulSize; i += 0x10)
  {
    if((i % 0x10) == 0)
      fprintf(pFile, "\n0x%8p   ", (i + szData));

    for(j = 0; ((i + j) < ulSize) && (j < 0x10); j++)
      fprintf(pFile, "%.2x ", (unsigned char)pBuff[i+j]);

    for(; j < 0x10; j++)
      fprintf(pFile, "   ");

    fprintf(pFile, "  ");

    for(j = 0; ((i + j) < ulSize) && (j < 0x10); j++)
      fprintf(pFile, "%c", (unsigned char)pBuff[i+j] > ' ' ? pBuff[i+j] : '.');
  }
  fprintf(pFile, "\n\n");
  fflush(pFile);
}


int main()
{
  FILE* pFile = fopen("dump.txt", "wt+");
  if (!pFile)
  {
    perror("error while opening file");
    return 1;
  }

  const char* szData = "1234567890qwertyuiop"; // received data
  unsigned long ulSize = (unsigned long)strlen(szData); // data length just for example

  dump(pFile, szData, ulSize);
  fclose(pFile);
}

output format (pointer, hex, char):

0x0x400a9c   31 32 33 34 35 36 37 38 39 30 71 77 65 72 74 79   1234567890qwerty
0x0x400aac   75 69 6f 70                                       uiop

Answer 3

sprintf uses the %x conversion for hex, so you'd typically use something like this:

cvt2hex(unsigned len, char const *input, char *output) { 
    int i;
    for (i=0; i<len; i++)
        sprintf(output+i*3, "%2.2x ", input[i]);
}

Of course, output needs to point to enough memory to hold the converted data. You'll typically want to insert a new-line after every 16 or 32 bytes, or somewhere in that vicinity.

Answer 4

另一种方法是对char（hh）使用长度修饰符：

printf("%hhx", c);