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I am new to C and I have already tried many ways to convert char* variable which store binary representation into hex value.

The variable is for example:

0110110000001110110000010100111000110011110110110111000110111000

which stands for

6C 0E C1 4E 33 DB 71 B8

where

0110- 6, 1100 - C, 0000 - 0, 1110 - E and so on...

However when I want to use fprintf format or strtol, which I found recommended for this kind of problems, I get:

char* lm_bin = "0110110000001110110000010100111000110011110110110111000110111000"; //convert to dec int lm_dec = (int)strtol(lm_bin, NULL, 2); char lm_hex[12]; //convert to hex sprintf(lm_hex, "%x", lm_dec); fprintf(stderr, "binary %s", lm_bin); fprintf(stderr, "hex %s", lm_hex);

the output is:

binary 0110110000001110110000010100111000110011110110110111000110111000 hex 33db71b8

which is not correct. Can anyone point me where I am making a mistake?

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    Why are you trying to squeeze 16 characters of hex into a 12 byte string, which can only really handle 11 characters plus a null terminator. It also helps readability of output if you include newlines at appropriate points. And you would probably do better with with unsigned long long and strtoull() — int won't hold 16 hex digits on most machines. Commented Apr 4, 2018 at 6:04
  • 2
    int is probably not wide enough. Your platform seems to have 32 bit ints and your input is 64 bits. Commented Apr 4, 2018 at 6:05

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Why are you trying to squeeze 16 characters of hex into a 12 byte string, which can only really handle 11 characters plus a null terminator. It also helps readability of output if you include newlines at appropriate points. And you would probably do better with with unsigned long long and strtoull() — int won't hold 16 hex digits on most machines. It is also conventional to write expected output on standard output; use standard error for error messages.

Putting those changes together yields an MCVE (Minimal, Complete, Verifiable Example) like this:

#include <stdio.h> #include <stdlib.h> int main(void) { const char lm_bin[] = "0110110000001110110000010100111000110011110110110111000110111000"; unsigned long long lm_dec = strtoull(lm_bin, NULL, 2); char lm_hex[17]; sprintf(lm_hex, "%llx", lm_dec); printf("binary %s\n", lm_bin); printf("hex %s\n", lm_hex); return 0; }

And the output from that is what you sought, I believe:

binary 0110110000001110110000010100111000110011110110110111000110111000 hex 6c0ec14e33db71b8

That code doesn't check for conversion errors and could use snprintf() instead of sprintf(), and could do all the printing in a single call to printf() — and doesn't need to use the string for the hex-formatted output (it could format lm_dec directly). So, there's lots of room for changes and improvements in the code.

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ahhh it is so much more to learn. I missed not only long long int but also long long hex. Naturally Your code works like charm. Thank You very much !

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