Simple build number counter.

buildnum.c

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

int main(int argc, char **argv) {
    if(argc != 2) {
        printf("Usage: buildnum <file>\n");
        return 1;
    }

    FILE *f = fopen(argv[1], "rb");
    if(!f) {
        f = fopen(argv[1], "wb");
        if(!f) {
            printf("failed to open/create file\n");
            return 1;
        }
    }

    int buildnumber = -1;
    int filled = fscanf(f, "%d", &buildnumber);
    if(filled != 1) {
        buildnumber = 1;
    } else {
        buildnumber++;
    }

    f = freopen(argv[1], "wb", f);
    fprintf(f, "%d", buildnumber);
    fflush(f);

    return 0;
}