CODEWITHSUNDEEP
c
jamesatha
jamesatha

Reputation: 7600

Determining if a file exists in C based on the string path

I have a C string that I want to use to open that file. How do I determine if the file exists?

Upvotes: 1

Views: 297

Answers (4)

mr.stobbe
mr.stobbe

Reputation: 612

Everyone's answers are valid (with minor tweeks) here but make some assumptions. First, if it actually a file your checking or is it possibly a file/directory/symlink/fifo/socket/etc. If it's just a file, the fopen(), stat() and access() solutions won't work.

fopen() will succeed on nearly all object types in many operating systems (including a valid directory), while stat() and access() will most certainly success regardless of filesystem object type in all operating systems (they will always succeed is a filesystem object exists and is accessable in the current security context [logged in user]). Even worse, windows compilers will treat stat differently (because they either link to msvc's lib or they inline their own implemenation).

Sadly, your best approach (if determining if a file exists and you want to be portable) is something like...

#ifdef _WIN32
    #include <windows.h>
#else
    #include <sys/stat.h>
    #include <unistd.h>
#endif

int file_exists(const char* filename) {
    #ifdef _WIN32
        HANDLE h = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, 0);
        if (h == INVALID_HANDLE_VALUE)
            return 0;
        int res = 0;
        if (GetFileType(h) == FILE_TYPE_DISK)
            res = 1;
        CloseHandle(h);
        return res;
    #else
        struct stat st;
        if (stat(filename, &st) == -1)
            return 0;
        return S_ISREG(st.st_mode);
    #endif
    return 0;
}

Upvotes: 1

poundifdef
poundifdef

Reputation: 19353

You could also use stat

#include <stdio.h>
#include <sys/stat.h>

int main(int argc, char *argv[]) {

   struct stat s;

   if (stat("/path/to/file", &s) == -1) {
      printf("Invalid path\n");
   } else {
      printf("Valid path\n");
   }   

   return 0;

}

This does not tell you whether your program has permissions to read or write the file (fopen() is good for that) but this will tell you whether or not the path exists.

Upvotes: 0

Adrian Cornish
Adrian Cornish

Reputation: 23858

Use the function called access()

if(access(file_path, F_OK)==0)
    //file exists
else
    // file does not exists

Upvotes: 5

Peter Shinners
Peter Shinners

Reputation: 3766

In most cases it is easiest to just open the file for writing. If there is a problem you will get a NULL file handle back.

#include <stdio.h>
int fileExists(const char* path) {
    FILE* f = fopen(path, "rb");
    if (!f) {
        return 0;
    }
    fclose(path);
    return 1;
}

Of course, if you are going to want to read from the file, you shouldn't fclose() the handle immediately.

Upvotes: 0

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