C ++ FileIO复制-VS-系统（“cp file1.x file2.x） [英] C++ FileIO Copy -VS- System("cp file1.x file2.x)

问题描述

编写文件复制例程会更快/更有效率，还是应该对cp执行系统调用？

Would it be quicker/efficient to write a file copy routine or should I just execute a System call to cp?

（文件系统可能不同[nfs，

(The file system could differ [nfs, local, reiser, etc], however it would always be on a CentOS linux system)

推荐答案

通过使用启用 外壳 > system（） 功能效率不高且不是很安全。

Invoking a shell by using system () function is not efficient and not very secure.

在Linux中复制文件的最有效的方法是使用 sendfile（） 系统调用。
在Windows上， CopyFile（） API函数或其相关变体之一。

The most efficient way to copy a file in Linux is to use sendfile () system call. On Windows, CopyFile () API function or one of its related variants should be used.

示例使用 sendfile ：

#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int main (int argc, char* argv[])
{
 int read_fd;
 int write_fd;
 struct stat stat_buf;
 off_t offset = 0;

 /* Open the input file. */
 read_fd = open (argv[1], O_RDONLY);
 /* Stat the input file to obtain its size. */
 fstat (read_fd, &stat_buf);
 /* Open the output file for writing, with the same permissions as the
   source file. */
 write_fd = open (argv[2], O_WRONLY | O_CREAT, stat_buf.st_mode);
 /* Blast the bytes from one file to the other. */
 sendfile (write_fd, read_fd, &offset, stat_buf.st_size);
 /* Close up. */
 close (read_fd);
 close (write_fd);

 return 0;
}

如果您不希望代码与平台相关，更便携的解决方案 - Boost文件系统库或 std :: fstream 。

If you do not want your code to be platform dependent, you may stick with more portable solutions - Boost File System library or std::fstream.

使用Boost的示例href =http://www.boost.org/doc/libs/1_44_0/libs/filesystem/v2/test/operations_test.cpp>更完整的示例）：

Example using Boost (more complete example):

copy_file (source_path, destination_path, copy_option::overwrite_if_exists);

使用C ++的示例 std :: fstream ：

ifstream f1 ("input.txt", fstream::binary);
ofstream f2 ("output.txt", fstream::trunc|fstream::binary);
f2 << f1.rdbuf ();

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