How to get file extension from string in C++

Is this too simple of a solution?

#include <iostream>
#include <string>

int main()
{
  std::string fn = "filename.conf";
  if(fn.substr(fn.find_last_of(".") + 1) == "conf") {
    std::cout << "Yes..." << std::endl;
  } else {
    std::cout << "No..." << std::endl;
  }
}

You have to make sure you take care of file names with more then one dot. example: c:\.directoryname\file.name.with.too.many.dots.ext would not be handled correctly by strchr or find.

My favorite would be the boost filesystem library that have an extension(path) function

The best way is to not write any code that does it but call existing methods. In windows, the PathFindExtension method is probably the simplest.

So why would you not write your own?

Well, take the strrchr example, what happens when you use that method on the following string "c:\program files\AppleGate.Net\readme"? Is ".Net\readme" the extension? It is easy to write something that works for a few example cases, but can be much harder to write something that works for all cases.

Assuming you have access to STL:

std::string filename("filename.conf");
std::string::size_type idx;

idx = filename.rfind('.');

if(idx != std::string::npos)
{
    std::string extension = filename.substr(idx+1);
}
else
{
    // No extension found
}

Edit: This is a cross platform solution since you didn't mention the platform. If you're specifically on Windows, you'll want to leverage the Windows specific functions mentioned by others in the thread.