std::experimental::filesystem::resize_file
From cppreference.com
< cpp | experimental | fs
| Defined in header <experimental/filesystem>
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| void resize_file( const path& p, std::uintmax_t new_size ); void resize_file( const path& p, std::uintmax_t new_size, error_code& ec ); |
(filesystem TS) | |
Changes the size of the regular file named by p as if by POSIX truncate: if the file size was previously larger than new_size, the remainder of the file is discarded. If the file was previously smaller than new_size, the file size is increased and the new area appears as if zero-filled.
Parameters
| p | - | path to resize |
| new_size | - | size that the file will now have |
| ec | - | out-parameter for error reporting in the non-throwing overload |
Return value
(none)
Exceptions
The overload that does not take an error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking an 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. This overload hasnoexcept specification:
noexcept
Notes
On systems that support sparse files, increasing the file size does not increase the space it occupies on the file system: space allocation takes place only when non-zero bytes are written to the file.
Example
Demonstrates the effect of creating a sparse file on the free space.
Run this code
#include <experimental/filesystem> #include <fstream> #include <iostream> namespace fs = std::experimental::filesystem; int main() { fs::path p = fs::temp_directory_path() / "example.bin"; std::ofstream(p).put('a'); std::cout << "File size: " << fs::file_size(p) << '\n' << "Free space: " << fs::space(p).free << '\n'; fs::resize_file(p, 64*1024); // resize to 64 KB std::cout << "File size: " << fs::file_size(p) << '\n' << "Free space: " << fs::space(p).free << '\n'; fs::remove(p); }
Possible output:
File size: 1 Free space: 31805444096 File size: 65536 Free space: 31805444096
See also
| returns the size of a file (function) | |
| determines available free space on the file system (function) |