30 Input/output library [input.output]

30.10 File systems [filesystems]

30.10.15 Filesystem operation functions [fs.op.funcs]

30.10.15.14 File size [fs.op.file_size]

uintmax_t file_size(const path& p);
uintmax_t file_size(const path& p, error_code& ec) noexcept;

Returns:

(1.1)
If exists(p) is false, an error is reported ([fs.err.report]).
(1.2)
Otherwise, if is_regular_file(p), the size in bytes of the file p resolves to, determined as if by the value of the POSIX stat structure member st_size obtained as if by POSIX stat().
(1.3)
Otherwise, the result is implementation-defined.

The signature with argument ec returns static_cast<uintmax_t>(-1) if an error occurs.

Throws: As specified in [fs.err.report].