C - Why fopen doesn't work?

Question

I have this very simple code:

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

int main (void)
    {
    FILE * file_ptr = NULL;

    file_ptr = fopen ("file.txt", "r");

    if (file_ptr == NULL)
        {
        puts ("Error!");
        return EXIT_FAILURE;
        }
    else
        {
        puts ("O.k.!");
        }

    return EXIT_SUCCESS;
    }

Output:

Error!

Why fopen doesn't work? The file is not protected, not opened elsewhere and is stored in the same folder as the *.exe of this program. I also tried it with giving the complete path to the file and with an array, in which the filename is stored. Everytime it puts out "Error!".

What's going on??

I'm using Eclipse Neon.2 Release (4.6.2) with newest cygwin gcc compiler on Windows 10 64bit.

Thank you for your help!

Answer 1

The problem was solved by changing the fopen to

file_ptr = fopen("xxyyzzqq.txt", "w");

and then searching the hard drive to see where the file was created.

Turns out that the file was created in the project source directory, and not the debug directory (where the .exe file is), unlike the old installation which used the debug directory as the working directory.

Answer 2

perror might help.

FILE *file_ptr = fopen("file.txt", "r");
if (!file_ptr) {
  perror("fopen");
} else {
  printf("It's working!");
}

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