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Well I threw together a test program that ran each of these methods 100,000 times, half on files that existed and half on files that didn't.

#include 
   
    #include 
    
     #include 
     
      inline bool exists_test0 (const std::string& name) {
       ifstream f(name.c_str());    return f.good();}inline bool exists_test1 (const std::string& name) {
       if (FILE *file = fopen(name.c_str(), "r")) {
           fclose(file);        return true;    } else {
           return false;    }   }inline bool exists_test2 (const std::string& name) {
       return ( access( name.c_str(), F_OK ) != -1 );}inline bool exists_test3 (const std::string& name) {
     struct stat buffer;     return (stat (name.c_str(), &buffer) == 0); }
     
    
   

Results for total time to run the 100,000 calls averaged over 5 runs,

Method exists_test0 (ifstream): **0.485s**Method exists_test1 (FILE fopen): **0.302s**Method exists_test2 (posix access()): **0.202s**Method exists_test3 (posix stat()): **0.134s**

The stat() function provided the best performance on my system (Linux, compiled with g++), with a standard fopen call being your best bet if you for some reason refuse to use POSIX functions.

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