openbsd.c

#include <ctype.h>
#include <stdio.h>

int openbsd_check(const char* line) {
    if (isdigit((int)*line) && *(line + 1) == '.' &&
        isdigit((int)*line+2) && *(line + 3) == '.' &&
        isdigit((int)*line+4) && isspace((int)*(line + 5)))
        return 1;
    else
        return 0;
}

int regular_check(const char* line) {
    if (isdigit((int)*line) && *(line + 1) == '.' &&
        isdigit((int)*(line+2)) && *(line + 3) == '.' &&
        isdigit((int)*(line+4)) && isspace((int)*(line + 5)))
        return 1;
    else
        return 0;
}

int main() {
    const char* valid_line = "5.4.0 ";
    const char* nasty_line = "5.?.! ";

    printf("OpenBSD check for a valid line: %d\n", openbsd_check(valid_line));
    printf("OpenBSD check for an invalid line: %d\n", openbsd_check(nasty_line));

    printf("Regular check for a valid line: %d\n", regular_check(valid_line));
    printf("Regular check for an invalid line: %d\n", regular_check(nasty_line));

    /*
     * $ gcc -O2 openbsd.c -o openbsd
     * $ ./openbsd
     * OpenBSD check for a valid line: 1
     * OpenBSD check for an invalid line: 1
     * Regular check for a valid line: 1
     * Regular check for an invalid line: 0
     */
}