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std::filesystem::file_size(3) | C++ Standard Libary | std::filesystem::file_size(3) |
NAME¶
std::filesystem::file_size - std::filesystem::file_size
Synopsis¶
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 static_cast<std::uintmax_t>(-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 std::error_code& parameter
throws
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. 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.
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 i{};
double mantissa = hr.size;
for (; mantissa >= 1024.; mantissa /= 1024., ++i) { }
mantissa = std::ceil(mantissa * 10.) / 10.;
os << mantissa << "BKMGTPE"[i];
return i == 0 ? os : os << "B (" << hr.size <<
')';
}
};
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";
fs::file_size("/dev");
} catch(fs::filesystem_error& e) {
std::cout << e.what() << '\n';
}
std::error_code ec;
for (fs::path bin: {"cat", "mouse"}) {
bin = "/bin"/bin;
std::uintmax_t size = fs::file_size(bin, ec);
if (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
See also¶
resize_file changes the size of a regular file by truncation or
zero-fill
(C++17) (function)
space determines available free space on the file system
(C++17) (function)
file_size returns the size of the file to which the directory entry refers
(public member function of std::filesystem::directory_entry)
2022.07.31 | http://cppreference.com |