C++ Cookbook

10.6. Getting Information About a File

Problem

You want information about a file, such as its size, device, last modification time, etc.

Solution

Use the C system call stat in <sys/stat.h>. See Example 10-8 for a typical use of stat that prints out a few file attributes.

Example 10-8. Obtaining file information

#include <iostream>
#include <ctime>
#include <sys/types.h>
#include <sys/stat.h>
#include <cerrno>
#include <cstring>

int main(int argc, char** argv )
{
   struct stat fileInfo;

   if (argc < 2) {
      std::cout << "Usage: fileinfo <file name>\n";
      return(EXIT_FAILURE);
   }

   if (stat(argv[1], &fileInfo) != 0) {  // Use stat() to get the info
      std::cerr << "Error: " << strerror(errno) << '\n';
      return(EXIT_FAILURE);
   }

   std::cout << "Type:         : ";
   if ((fileInfo.st_mode & S_IFMT) == S_IFDIR) { // From sys/types.h
      std::cout << "Directory\n";
   } else {
      std::cout << "File\n";
   }

   std::cout << "Size          : " <<
      fileInfo.st_size << '\n';               // Size in bytes
   std::cout << "Device        : " <<
      (char)(fileInfo.st_dev + 'A') << '\n';  // Device number
   std::cout << "Created       : " <<
      std::ctime(&fileInfo.st_ctime);         // Creation time
   std::cout << "Modified      : " <<
      std::ctime(&fileInfo.st_mtime);         // Last mod time
}

Discussion

The C++ standard library supports manipulation of file content with streams, but it has no built-in support for reading or altering the metadata the OS maintains about a file, such as its size, ownership, permissions, various timestamps, and other information. However, standard C contains a number of standard system ...