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std::filesy...resize_file(3) C++ Standard Libary std::filesy...resize_file(3) NAME std::filesystem::resize_file - std::filesystem::resize_file Synopsis Defined in header <filesystem> void resize_file( const std::filesystem::path& p, std::uintmax_t new_size ); void resize_file( const std::filesystem::path& p, (since C++17) std::uintmax_t new_size, std::error_code& ec ) noexcept; Changes the size of the regular file named by p as if by POSIX trun- cate: 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 in- creased 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 a std::error_code& parameter throws filesystem::filesystem_error on underlying OS API errors, con- structed with p as the first path argument and the OS error code as the error code argu- ment. 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. 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 <iostream> #include <fstream> #include <filesystem> namespace fs = std::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 file_size returns the size of a file (C++17) (function) space determines available free space on the file system (C++17) (function) http://cppreference.com 2022.07.31 std::filesy...resize_file(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Example | Possible output: | See also
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