how to get hexdump of a structure data

Question

 ....  finalize(char *hdrs, sendip_data *headers[], int index,                     sendip_data *data, sendip_data *pack)  {   ........ 

For debugging purposes I want a hex dump of the data and pack structures, which are of type sendip_data, a really complex structure. Actually they contain some binary information so I am not sure whether output of my project is correct or not. So for debugging purposes, I want to write the data into a file so that I can use hexdump as follows -

$hexdump -C file.txt 

Also as this is a run time generation of a n/w packet so I am also not sure about the length of data and pack structure which I think fread / fwrite will require ..So please suggest me something.

Answer 1

The following code will give you a hex dump of arbitrary memory from within your code.

#include <stdio.h>  // Usage: //     hexDump(desc, addr, len, perLine); //         desc:    if non-NULL, printed as a description before hex dump. //         addr:    the address to start dumping from. //         len:     the number of bytes to dump. //         perLine: number of bytes on each output line.  void hexDump (     const char * desc,     const void * addr,     const int len,     int perLine ) {     // Silently ignore silly per-line values.      if (perLine < 4 || perLine > 64) perLine = 16;      int i;     unsigned char buff[perLine+1];     const unsigned char * pc = (const unsigned char *)addr;      // Output description if given.      if (desc != NULL) printf ("%s:\n", desc);      // Length checks.      if (len == 0) {         printf("  ZERO LENGTH\n");         return;     }     if (len < 0) {         printf("  NEGATIVE LENGTH: %d\n", len);         return;     }      // Process every byte in the data.      for (i = 0; i < len; i++) {         // Multiple of perLine means new or first line (with line offset).          if ((i % perLine) == 0) {             // Only print previous-line ASCII buffer for lines beyond first.              if (i != 0) printf ("  %s\n", buff);              // Output the offset of current line.              printf ("  %04x ", i);         }          // Now the hex code for the specific character.          printf (" %02x", pc[i]);          // And buffer a printable ASCII character for later.          if ((pc[i] < 0x20) || (pc[i] > 0x7e)) // isprint() may be better.             buff[i % perLine] = '.';         else             buff[i % perLine] = pc[i];         buff[(i % perLine) + 1] = '\0';     }      // Pad out last line if not exactly perLine characters.      while ((i % perLine) != 0) {         printf ("   ");         i++;     }      // And print the final ASCII buffer.      printf ("  %s\n", buff); }  // Very simple test harness.  int main (int argc, char *argv[]) {     char my_str[] = "a char string greater than 16 chars";     hexDump ("my_str", &my_str, sizeof (my_str), 16);     return 0; } 

You pass into hexDump a description, memory address, length, and how many bytes you want on each line.

It will output a hex dump (including character data) for examination. When you run it with the included main, the output is:

my_str:   0000  61 20 63 68 61 72 20 73 74 72 69 6e 67 20 67 72  a char string gr   0010  65 61 74 65 72 20 74 68 61 6e 20 31 36 20 63 68  eater than 16 ch   0020  61 72 73 00                                      ars.