std::filesystem::file_size
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< cpp | filesystem
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Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Filesystem library
filesystem::file_size
Defined in header
<filesystem>
std::uintmax_t file_size( const std::filesystem::path & p );
(1)
(since C++17)
std::uintmax_t file_size( const std::filesystem::path & p,
std::error_code & ec ) noexcept;
(2)
(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 static_cast<std::uintmax_t >(-1) on errors.
[edit] Parameters
p
-
path to examine
ec
-
out-parameter for error reporting in the non-throwing overload
[edit] Return value
The size of the file, in bytes.
[edit] Exceptions
Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.
1) Throws std::filesystem::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.
2) Sets a std::error_code & parameter to the OS API error code if an OS API call fails, and executes ec.clear () if no errors occur.
[edit] Example
Run this code
#include <cmath> #include <filesystem> #include <fstream> #include <iostream> namespace fs = std::filesystem; struct HumanReadable { std::uintmax_t size{}; private: friend std::ostream & operator<<(std::ostream & os, HumanReadable hr) { int o{}; double mantissa = hr.size; for (; mantissa >= 1024.; mantissa /= 1024., ++o); os << std::ceil (mantissa * 10.) / 10. << "BKMGTPE"[o]; return o ? os << "B (" << hr.size << ')' : os; } }; int main(int, char const* argv[]) { fs::path example = "example.bin"; fs::path p = fs::current_path() / example; std::ofstream (p).put('a'); // create file of size 1 std::cout << example << " size = " << fs::file_size(p) << '\n'; fs::remove(p); p = argv[0]; std::cout << p << " size = " << HumanReadable{fs::file_size(p)} << '\n'; try { std::cout << "Attempt to get size of a directory:\n"; [[maybe_unused]] auto x_x = fs::file_size("/dev"); } catch (fs::filesystem_error& e) { std::cout << e.what() << '\n'; } for (std::error_code ec; fs::path bin : {"cat", "mouse"}) { bin = "/bin"/bin; if (const std::uintmax_t size = fs::file_size(bin, ec); ec) std::cout << bin << " : " << ec.message() << '\n'; else std::cout << bin << " size = " << HumanReadable{size} << '\n'; } }
Possible output:
"example.bin" size = 1 "./a.out" size = 22KB (22512) Attempt to get size of a directory: filesystem error: cannot get file size: Is a directory [/dev] "/bin/cat" size = 50.9KB (52080) "/bin/mouse" : No such file or directory