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 ...