CODEWITHSUNDEEP
c
Andrey Bushman
Andrey Bushman

Reputation: 12516

How can I check existence of the file via C89?

I apologize for my bad English.

Different files can has different permissions. For example I can have not permission for a file read/write, but this file is exists. How can I check existence of the such file via C89?

Thank you. Best Regards

Upvotes: 1

Views: 172

Answers (3)

md5
md5

Reputation: 23737

There is no portable way to determine wheter a file exists; you have to resort to a system-specific method (such as access or stat from POSIX.1). Sometimes, it may not be possible to check the existence of a named file, because you don't have permission to read the directory that may contain it.

Upvotes: 2

user529758
user529758

Reputation:

In pure ISO C89, there's no good and portable way of checking the existence of a file. However, there are implementation-defined solutions or other OS-specific extensions for that. For example:

int file_exists(const char *name)
{
     return access(name, F_OK) == 0;
}

Note that this (access()) is not part of C89, but most systems one cares about have it.

Or there is

int file_exists(const char *name)
{
    FILE *f = fopen(name, "r");
    if ((f == NULL) && (errno == ENOENT)) {
        return 0;
    }
    fclose(f);
    return 1;
}

This is again not C89, but most C89-conformant systems will provide ENOENT.

Another option is to use the stat() function, it also returns -1 and sets errno to ENOENT if the file doesn't exist.

Upvotes: 3

Alexey Frunze
Alexey Frunze

Reputation: 62106

If you stick to C89, there's no universal way of checking for file existence.

There are some standard functions outside of C89, POSIX functions:

stat()

fstat()

At any rate, it depends on the OS since the language itself does not provide such functionality.

Upvotes: 2

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