头文件 unistd.h

if(access(file_name, F_OK ) != -1 ) 
{
    // file exists
} 
else 
{
    // file doesn't exist
}

You can also use R_OK, W_OK, and X_OK in place of F_OK to check for read permission, write permission, and execute permission (respectively) rather than existence, and you can OR any of them together (i.e. check for both read and write permission using R_OK|W_OK)

Update: Note that on Windows, you can't use W_OK to reliably test for write permission, since the access function does not take DACLs into account. access( fname, W_OK ) may return 0 (success) because the file does not have the read-only attribute set, but you still may not have permission to write to the file.

出处：

https://stackoverflow.com/questions/230062/whats-the-best-way-to-check-if-a-file-exists-in-c

Graeme Perrow