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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, (1) (since C++17) std::uintmax_t new_size ); void resize_file( const std::filesystem::path& p, std::uintmax_t new_size, (2) (since C++17) 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 Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails. 1) Throws std::filesystem::filesystem_error on underlying OS API er- rors, 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. 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 creating a sparse file has on the free space. // Run this code #include <filesystem> #include <fstream> #include <iostream> #include <locale> int main() { auto p = std::filesystem::temp_directory_path() / "example.bin"; std::ofstream{p}.put('a'); std::cout.imbue(std::locale{"en_US.UTF8"}); std::cout << "File size: " << std::filesystem::file_size(p) << '\n' << "Free space: " << std::filesystem::space(p).free << '\n'; std::filesystem::resize_file(p, 64*1024); // resize to 64 KB std::cout << "File size: " << std::filesystem::file_size(p) << '\n' << "Free space: " << std::filesystem::space(p).free << '\n'; std::filesystem::remove(p); } Possible output: File size: 1 Free space: 42,954,108,928 File size: 65,536 Free space: 42,954,108,928 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 2024.06.10 std::filesy...resize_file(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Example | Possible output: | See also
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