title: Sorting files with boost filesystem
body: <p>here is my problem: I got a stack of files that have names like "_X1.bla.txt", "_X101.bla.txt", _X47.bla.txt" that i read in with boost::filesystem and added to a std::vector . </p>
  
  <p>As you see from the example, the names do not start with the numbers. In this example, the result shoud be 1, 47, 101. If you got tell me how i could extract the numbers from the files i should be able to autosort the files by myself. </p>
  
  <p>Best
  hu dao</p>