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In this conclusion to a five-part article series on streams and files in C++, you will learn how to extract a filename from a full path, and more. This article is excerpted from chapter 10 of the C++ Cookbook, written by Ryan Stephens, Christopher Diggins, Jonathan Turkanis and Jeff Cogswell (O'Reilly; ISBN: 0596007612). Copyright 2007 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.

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By: O'Reilly Media
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November 13, 2008
TABLE OF CONTENTS:
  1. · Paths and Files
  2. · 10.15 Extracting a Path from a Full Path and Filename
  3. · 10.16 Replacing a File Extension
  4. · 10.17 Combining Two Paths into a Single Path

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Paths and Files
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10.14 Extracting a Filename from a Full Path

Problem

You have the full path of a filename, e.g., d:\apps\src\foo.c, and you need to get the filename, foo.c.

Solution

Employ the same technique as the previous recipe and use rfind and substr to find and get what you want from the full pathname. Example 10-21 shows how.

Example 10-21. Extracting a filename from a path

#include <iostream>
#include <string>

using std::string;

string getFileName(const string& s) {

  char sep = '/';

#ifdef _WIN32
  
sep = '\';
#endif

   size_t i = s.rfind(sep, s.length());
   if (i != string::npos) {
      return(s.substr(i+1, s.length() - i));
   }

   return("");
}

int main(int argc, char** argv) {

   string path = argv[1];

   std::cout << "The file name is "" << getFileName(path) << ""\n";
}

Discussion

See the previous recipe for details on how rfind and substr work. The only thing noteworthy about Example 10-21 is that, as you probably are already aware, Windows has a path separator that is a backslash instead of a forward-slash, so I added an #ifdef to conditionally set the path separator.

The path class in the Boost Filesystem library makes getting the last part of a full pathname--which may be a file or directory name--easy with the path::leaf member function. Example 10-22 shows a simple program that uses it to print out whether a path refers to a file or directory.

Example 10-22. Getting a filename from a path

#include <iostream>
#include <cstdlib>
#include <boost/filesystem/operations.hpp>

using namespace std;
using namespace boost::filesystem;

int main(int argc, char** argv) {

   // Parameter checking...

   try {
      path p = complete(path(argv[1], native));
      cout << p.leaf() << " is a "
          
<< (is_directory(p) ? "directory" : "file") << endl;
   }
   catch (exception& e) {
     
cerr << e.what() << endl;
   }

  return(EXIT_SUCCESS);
}

See the discussion in Recipe 10.7 for more information about the path class.

See Also

Recipe 10.15


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