std::filesystem::file_size (3) - Linux Manuals
Defined in header <filesystem>
std::uintmax_t file_size( const std::filesystem::path& p );
std::uintmax_t file_size( const std::filesystem::path& p, (1) (since C++17)
std::error_code& ec ) noexcept;
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.
p - path to examine
ec - out-parameter for error reporting in the non-throwing overload
The size of the file, in bytes.
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.
// Run this code
resize_file changes the size of a regular file by truncation or zero-fill
space determines available free space on the file system
file_size (public member function of std::filesystem::directory_entry)