check if a file exists

access.cc

#include <unistd.h>

// Check whether file exist
// http://stackoverflow.com/questions/230062/whats-the-best-way-to-check-if-a-file-exists-in-c-cross-platform

if( access( fname, 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)
*/