std::experimental::filesystem::exists (3) - Linux Manuals

std::experimental::filesystem::exists: std::experimental::filesystem::exists

NAME

std::experimental::filesystem::exists - std::experimental::filesystem::exists

Synopsis

Defined in header <experimental/filesystem>
bool exists( file_status s ) (1) (filesystem TS)
bool exists( const path& p ); (2) (filesystem TS)
bool exists( const path& p, error_code& ec )

Checks if the given file status or path corresponds to an existing file or directory.
1) Equivalent to status_known(s) && s.type() != file_type::not_found.
2) Equivalent to exists(status(p)) or exists(status(p, ec)) (symlinks are followed). The non-throwing overload returns false if an error occurs.

Parameters

s - file status to check
p - path to examine
ec - out-parameter for error reporting in the non-throwing overload

Return value

true if the given path or file status corresponds to an existing file or directory, false otherwise.

Exceptions

1)
noexcept specification:
noexcept
2) The overload that does not take a error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking a error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. This overload has
noexcept specification:
noexcept

Notes

The information provided by this function is usually also provided as a byproduct of directory iteration. During directory iteration, calling exists(*iterator) is less efficient than exists(iterator->status())

Example

// Run this code

  #include <iostream>
  #include <fstream>
  #include <cstdint>
  #include <experimental/filesystem>
  namespace fs = std::experimental::filesystem;

  void demo_exists(const fs::path& p, fs::file_status s = fs::file_status{})
  {
      std::cout << p;
      if(fs::status_known(s) ? fs::exists(s) : fs::exists(p))
          std::cout << " exists\n";
      else
          std::cout << " does not exist\n";
  }
  int main()
  {
      fs::create_directory("sandbox");
      std::ofstream("sandbox/file"); // create regular file
      fs::create_symlink("non-existing", "sandbox/symlink");

      demo_exists("sandbox");
      for(auto it = fs::directory_iterator("sandbox"); it != fs::directory_iterator(); ++it)
          demo_exists(*it, it->status()); // use cached status from directory entry
      fs::remove_all("sandbox");
  }

Output:

  "sandbox" exists
  "sandbox/file" exists
  "sandbox/symlink" does not exist