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

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

NAME

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

Synopsis

Defined in header <filesystem>
bool exists( std::filesystem::file_status s ) noexcept; (1) (since C++17)
bool exists( const std::filesystem::path& p ); (2) (since C++17)
bool exists( const std::filesystem::path& p, std::error_code& ec ) noexcept;

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) Let s be a std::filesystem::file_status determined as if by status(p) or status(p, ec) (symlinks are followed), respectively. Returns exists(s). The non-throwing overload calls ec.clear() if status_known(s).

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

2) The overload that does not take a std::error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument. The overload taking a std::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. Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

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

 This section is incomplete
 Reason: switch to directory_entry::exists

// Run this code

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