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C++ Cookbook
book

C++ Cookbook

by D. Ryan Stephens, Christopher Diggins, Jonathan Turkanis, Jeff Cogswell
November 2005
Beginner to intermediate content levelBeginner to intermediate
594 pages
16h 23m
English
O'Reilly Media, Inc.
Content preview from C++ Cookbook

10.7. Copying a File

Problem

You need to copy one file to another in a portable manner, i.e., without using OS-specific APIs.

Solution

Use C++ file streams in <fstream> to copy data from one stream to another. Example 10-9 gives an example of a buffered stream copy.

Example 10-9. Copying a file

#include <iostream>
#include <fstream>

const static int BUF_SIZE = 4096;

using std::ios_base;

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

   std::ifstream in(argv[1],
      ios_base::in | ios_base::binary);  // Use binary mode so we can
   std::ofstream out(argv[2],            // handle all kinds of file
      ios_base::out | ios_base::binary); // content.
   
   // Make sure the streams opened okay...

   char buf[BUF_SIZE];

   do {
      in.read(&buf[0], BUF_SIZE);      // Read at most n bytes into
      out.write(&buf[0], in.gcount()); // buf, then write the buf to
   } while (in.gcount() > 0);          // the output.

   // Check streams for problems...

   in.close();
   out.close();
}

Discussion

Copying a file may appear to be a simple matter of reading from one stream and writing to another. But the C++ streams library is large, and there are a number of different ways to do the reading and the writing, so you should know a little about the library to avoid costly performance mistakes.

Example 10-9 runs fast because it buffers input and output. The read and write functions operate on entire buffers at a time—instead of a character-at-a-time copy loop—by reading from the input stream to the buffer and writing from the buffer to the output stream in chunks. They also do not do any kind ...

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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page