Check for nonzero data in a stream, quickly and without output. Answers http://superuser.com/q/559772/117590.

iszero-fast.cpp

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

    while (bytes_read = fread(buffer, 1, BUFFER_SIZE, file)) {
        for (long long i = 0; i < bytes_read; i++) {
            if (buffer[i] != 0) {
                printf("Nonzero byte encountered.\n");
                return 1;
            }
        }
    }
 
    int error = 0;
    if (error = ferror(file)) {
        fprintf(stderr, "Error reading file, code: %d\n", error);
        return -1;
    }
 
    printf("All bytes are zero.\n");
    return 0;
}

@rcorsari 5 years late, but ... yea, the faster way would be to use SIMD instructions to process multiple bytes at a time, using SIMD (SSE, AVX, etc.) intrinsics. But they're fairly complex to use. And a good compiler might generate them for a simple loop like this anyway.