Error Checks

File code checks whether fopen succeeded before using the stream.

error_checks.c

#include <stdio.h>

int main(void) {
    int createFile = ;
    const char *path = "error_checks_demo.txt";

    if (createFile) {
        FILE *created = fopen(path, "w");
        if (created != 0) {
            fputs("ok\n", created);
            fclose(created);
        }
    }

    FILE *file = fopen(path, "r");
    int opened = (file != 0);

    if (file != 0) {
        fclose(file);
        remove(path);
    }

    printf("opened=%d\n", opened);
    return 0;
}

#include <stdio.h>

int main(void) {
    int createFile = ;
    const char *path = "error_checks_demo.txt";

    if (createFile) {
        FILE *created = fopen(path, "w");
        if (created != 0) {
            fputs("ok\n", created);
            fclose(created);
        }
    }

    FILE *file = fopen(path, "r");
    int opened = (file != 0);

    if (file != 0) {
        fclose(file);
        remove(path);
    }

    printf("opened=%d\n", opened);
    return 0;
}

open failure `fopen` returns `0` when it cannot open the requested file.

guarded use Only pass a stream to I/O functions after checking that it is not `0`.