How to print out values from fread() in C

Question

I have a given simple code snippet that is supposed to generate a 128-bit encryption key. How do I print out the values to the console? Here's the code:

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

#define LEN 16 // 128 bits

void main()
{
    unsigned char *key = (unsigned char *) malloc(sizeof(unsigned char)*LEN);
    FILE* random = fopen("/dev/urandom", "r");
    fread(key, sizeof(unsigned char)*LEN, 1, random);
    fclose(random);
}

To be more specific: the instructions say: "Print out the numbers."

... and it is hardly worth malloc'ing a fixed sized small array: `unsigned char key[LEN] ;` would be more appropriate. In any event casting the return value of malloc is neither necessary or best practice in C. — Clifford, Oct 05 '19 at 18:56

score 0 · Accepted Answer · answered Oct 05 '19 at 18:52

0

Generating human readable binary data will usually involve hex or base64. Assuming hex code is acceptable:

for (int i=0 ; i<LEN ; i++ ) {
   printf("%02x", key[i]) ;
} ;
printf("\n") ;

answered Oct 05 '19 at 18:52

dash-o

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Clifford · Answer 2 · 2019-10-05T22:15:11.207

0

The most usual method of "human readable" presentation of binary data is to use hexadecimal, where each digit represents 4 bits.

for( int b = 0; b < len; b++ ) 
{
    printf( "%2.2X ", (int)key[b] ) ;
}

edited Oct 05 '19 at 22:15

answered Oct 05 '19 at 18:53

Clifford

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How to print out values from fread() in C

2 Answers2