Reserve disk space before writing a file for efficiency

Question

I have noticed a huge performance hit in one of my projects when logging is enabled for the first time. But when the log file limit is reached and the program starts writing

Answer 1

If you are using C++ 17, you should do it with std::filesystem::resize_file

Link

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.

#include 
#include 
#include 
#include 

namespace fs = std::filesystem;

int main()
{
    fs::path p = fs::current_path() / "example.bin"; 
    std::ofstream(p).put('a');
    fs::resize_file(p, 1024*1024*1024); // resize to 1 G
}