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Defined in header <filesystem> | ||
void resize_file(conststd::filesystem::path& p, std::uintmax_t new_size); | (1) | (since C++17) |
void resize_file(conststd::filesystem::path& p, std::uintmax_t new_size, | (2) | (since C++17) |
Changes the size of the regular file named byp as if by POSIXtruncate: if the file size was previously larger thannew_size, the remainder of the file is discarded. If the file was previously smaller thannew_size, the file size is increased and the new area appears as if zero-filled.
Contents |
| p | - | path to resize |
| new_size | - | size that the file will now have |
| ec | - | out-parameter for error reporting in the non-throwing overload |
(none)
Any overload not markednoexcept may throwstd::bad_alloc if memory allocation fails.
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.
Demonstrates the effect creating a sparse file has on the free space.
#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 KBstd::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: 1Free space: 42,954,108,928File size: 65,536Free space: 42,954,108,928
(C++17) | returns the size of a file (function)[edit] |
(C++17) | determines available free space on the file system (function)[edit] |
