Question

I can’t open a file in C, even though the file exists and isn’t used by any application. Can someone tell me what is causing this problem?

int main()
{
    FILE* oud;
    unsigned size;
    unsigned* bytes;
    char path[] = "C:\\Users\\Ruben\\Documents\\test.txt";
    errno_t error;

    if ((error  = fopen_s(&oud, path, "rb" )) == NULL)
    {
        perror(NULL);
        getchar();
        return -1;
    }

    fclose(oud);
    getchar();
    return 0;
    }
}

The output is: “No error”.

Answer 1

fopen_s() returns 0 on success, not NULL on failure:

Zero if successful; an error code on failure. See _doserrno, errno, _sys_errlist, and _sys_nerr for more information on these, and other, error codes.

The NULL macro is #defined to 0 (probably) which means if the file is opened the if() in the posted code is:

if (0 == 0)

which is obviously true. Change to:

if ((error = fopen_s(&oud, path, "rb" )) != 0)