Styjun

I am trying to print a fixed number of bytes (128) at at fixed file position (256) from a binary file to the screen.
However, the results show up look like:

For reference, I don't really know what's in the binary file; but I suspect that it's not squares.

Code is here:

int main() 

 FILE *file;
 char *buffer;

 file = fopen ( "binaryfile.bin" , "rb" );
 if (file==NULL) 
 
 fputs ("Couldn' open file",stderr);
 exit (-1);
 

 fseek (file , 0 , 256);
 buffer = (char*) malloc (sizeof(char)*128);
 fread (buffer,128,1,file);
 fwrite (buffer , sizeof(char)*128, 1, stdout);
 return 0;

This program is a mcve that shows how to read 128 bytes from a binary file and print each byte as a 2-digit hexadecimal value:

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

int main() 
 FILE *file;
 char *buffer;
 file = fopen("binaryfile.bin", "rb");
 if (file == NULL) 
 perror("Could not open file");
 exit(1);
 
 fseek(file, 256, SEEK_SET);
 buffer = malloc(sizeof(char) * 128);
 fread(buffer, sizeof(char), 128, file);
 for (int index = 0; index < 128; index++) 
 printf("%02X", ((unsigned int) buffer[index]) & 0x0FF);
 if (index % 8 == 7) 
 printf("n");
 
 else 
 printf(" ");
 
 
 printf("n");
 return 0;

Example Output

AD 0D 25 C8 74 AD D3 13
D5 00 62 EC CF 73 8E A4
61 2E 31 2F 70 ED D3 14
03 CC 06 B6 FB 77 FB ED
B4 0A 59 5F 50 00 61 59
D6 0B 21 F2 E6 1B 1A 07
DF 5E B8 32 17 D5 3E 29
0D 9E AE 47 D7 AF 86 4F
1E 75 6F EA C7 F7 A3 82
56 41 AA E8 02 42 91 D6
08 34 4F 63 40 9B 9C 06
0A 4E 65 30 90 7D 8A 4B
33 D1 50 9A 99 C5 F3 34
D9 A6 E0 2C 33 76 B3 DD
69 DF F9 30 8C 37 3A 51
9A 4F DB 81 81 F7 F5 F9

Note

This program is missing some error checking and does not free allocated memory. This code should not be used in a production environment.

fseek (file , 0 , 256); is wrong. The third argument to fseek is supposed to be one of SEEK_SET, SEEK_CUR or SEEK_END; the second is the offset. To set the file pointer to the 256th byte in the file, use:

fseek(file, 256, SEEK_SET);