What is the best way (short, using standard libraries and easy to understand) to do this in c++:
std::string s = magic_command("%4.2f", 123.456f)
I am aware of the snprintf malloc combo suggested for pure c in
writing formatted data of unknown length to a string (C programming)
but is there a better, less verbose, way to do this with c++?
I am also aware of the std::ostringstream method suggested in
Convert float to std::string in C++
but I want to pass a c format string such as "%4.2f", and I could not find a way to do this with ostringstream.
New answer 10 years later: C++20 std::format
Finally, this will be the superior choice once you can use it:
#include <format>
#include <string>
int main() {
std::cout << std::format("{:4.3}\n{:4.3}\n", 3.1, 3.1415);
}
Expected output:
3.1
3.14
This will therefore completely overcome the madness of modifying std::cout state.
The existing fmt library implements it for before it gets official support: https://github.com/fmtlib/fmt Install on Ubuntu 22.04:
sudo apt install libfmt-dev
Modify source to replace:
<format> with <fmt/core.h>std::format to fmt::formatmain.cpp
#include <iostream>
#include <fmt/core.h>
int main() {
std::cout << fmt::format("{:4.3}\n{:4.3}\n", 3.1, 3.1415);
}
and compile and run with:
g++ -std=c++11 -o main.out main.cpp -lfmt
./main.out
Output:
3.1
3.14
Old answer
All answers given are good since there seems to be no really standard way of doing what I want, I'll vote you all up, and accept my own sum up course of action: