std::filesystem::file_size

 Defined in header  std::uintmax_t file_size( const std::filesystem::path& p ); std::uintmax_t file_size( const std::filesystem::path& p,                           std::error_code& ec ) noexcept; (1) (since C++17)

If p does not exist, reports an error.

For a regular file p, returns the size determined as if by reading the st_size member of the structure obtained by POSIX stat (symlinks are followed)

The result of attempting to determine the size of a directory (as well as any other file that is not a regular file or a symlink) is implementation-defined.

The non-throwing overload returns -1 on errors.

Parameters

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

Return value

The size of the file, in bytes.

Exceptions

The overload that does not take a 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 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.

Example

#include <iostream>
#include <fstream>
#include <filesystem>
namespace fs = std::filesystem;
int main()
{
fs::path p = fs::current_path() / "example.bin";
std::ofstream(p).put('a'); // create file of size 1
std::cout << "File size = " << fs::file_size(p) << '\n';
fs::remove(p);

try {
fs::file_size("/dev"); // attempt to get size of a directory
} catch(fs::filesystem_error& e) {
std::cout << e.what() << '\n';
}
}

Possible output:

File size = 1
filesystem error: cannot get file size: Is a directory [/dev]

 resize_file(C++17) changes the size of a regular file by truncation or zero-fill (function) space(C++17) determines available free space on the file system (function) file_size returns the size of the file to which the directory entry refers (public member function of std::filesystem::directory_entry)