C program demonstrating byte array to hex string

hexstr.c

#include <stdio.h> // printf, sprintf, fprintf
#include <stdlib.h> // malloc

int main() {
    const unsigned char bytearr[] = { 0x12, 0x34, 0x56, 0x78 };
    const size_t arrlen = sizeof(bytearr);
    const size_t hexlen = 2; // hex representation of byte with leading zero
    const size_t outstrlen = arrlen * hexlen;

    char * outstr = malloc(outstrlen + 1);
    if (!outstr) {
        fprintf(stderr, "Failed to allocate memory\n");
        return 1;
    }

    // Create a string containing a hex representation of `bytearr`
    char * p = outstr;
    for (size_t i = 0; i < arrlen; i++) {
        p += sprintf(p, "%.2x", bytearr[i]);
    }

    printf("String variable contains:\n%s\n", outstr);
    free(outstr);
}