C++ How do I format a float with std::string?

Question

I would like to append a float to a string with the default iostream float format e.g 4.2f the following way:

std::string s;
s.append("float format: ");
s.append(std::to_string((float) 4.3)));
s.append(" : end");

I would like to find a function to generate the following result:

float format: 4.3f : end

But the code above gives me this result instead:

float format: 4.300000000000 : end

I have to format and then put in the string. I don't want to format when pushing on iostream.

the code above generates the following result: `float foatm: 4.300000000000 : end` — Romain-p, Jan 18 '18 at 02:12
Also related: https://stackoverflow.com/q/29200635/1896169 and https://stackoverflow.com/q/332111/1896169 — Justin, Jan 18 '18 at 02:16

score 2 · Accepted Answer · answered Jan 18 '18 at 02:18

2

Found a way using stringstream :) Then it uses the default ostream float format and pushes it to a string :)

std::stringstream ss;
std::string s;
ss << 3.4;
ss >> s;
std::cout << s.append("f") << std::endl;

generates the following output:

3.4f

answered Jan 18 '18 at 02:18

Romain-p

1 Answers1