What's the best way to check if a file exists in C?

Question

Is there a better way than simply trying to open the file?

int exists(const char *fname)
{
    FILE *file;
    if ((file = fopen(fname, \"r\")))
    {
               


        

Answer 1

Usually when you want to check if a file exists, it's because you want to create that file if it doesn't. Graeme Perrow's answer is good if you don't want to create that file, but it's vulnerable to a race condition if you do: another process could create the file in between you checking if it exists, and you actually opening it to write to it. (Don't laugh... this could have bad security implications if the file created was a symlink!)

If you want to check for existence and create the file if it doesn't exist, atomically so that there are no race conditions, then use this:

#include 
#include 

fd = open(pathname, O_CREAT | O_WRONLY | O_EXCL, S_IRUSR | S_IWUSR);
if (fd < 0) {
  /* failure */
  if (errno == EEXIST) {
    /* the file already existed */
    ...
  }
} else {
  /* now you can use the file */
}