Feature request: truncate output files

[BenjiHansell]

It seems that when I write to an output file which already exists, it is not truncated:

#include <fmt/os.h>

int main() {
  fmt::output_file("/path/to/file").print("AAAAA");
  // file contents is "AAAAA"
  fmt::output_file("/path/to/file").print("BBB");
  // file contents is "BBBAA", but it would be nice if it was "BBB"
}

output_file accepts some config flags, so I can hack around with undocumented FMT macros and get it to work how I want like this:

#include <fmt/os.h>

int main() {
  fmt::output_file("/path/to/file").print("AAAAA");
  // file contents is "AAAAA"
  fmt::output_file("/path/to/file").print("BBB", fmt::file::WRONLY | fmt::file::CREATE | FMT_POSIX(O_TRUNC));
  // file contents is "BBB"
}

Would it be possible to add an fmt::file::TRUNC option?

It might also be worth making that the default. I see no reason why someone would want fmt::file::WRONLY | fmt::file::CREATE (the current default) but be unhappy with fmt::file::WRONLY | fmt::file::CREATE | fmt::file::TRUNC. Although that would be a breaking change.

[vitaut]

Same as #2018. There is fmt::file::TRUNC already and it is the default.