Check for nonzero data in a stream. Answers http://superuser.com/q/559772/117590.

iszero.cpp

#include <cstdio>
 
#define BUFFER_SIZE 1024
 
int main() {
    FILE* file = stdin;
    char buffer[BUFFER_SIZE];
    long long bytes_read = 0;
    long long progress = 0;
    long long nonzero = 0;

    while (bytes_read = fread(buffer, 1, BUFFER_SIZE, file)) {
        for (long long i = 0; i < bytes_read; i++) {
            progress++;
            if (buffer[i] != 0) {
                nonzero++;
                printf("%lld: %x\n", progress, buffer[i]);
            }
        }
        fprintf(stderr, "%lld bytes processed\r", progress);
    }

    fprintf(stderr, "\n");
 
    int error = 0;
    if (error = ferror(file)) {
        fprintf(stderr, "Error reading file, code: %d\n", error);
        return -1;
    }
 
    printf("%lld nonzero characters encountered.\n", nonzero);
    return nonzero;
}