Preferred method for string formatting in c++?

Question

This is a bit verbose to my taste:

ostrstream ss;
ss << "Selected elements: " << i << "," << j << ".";
string msg(ss.str(), (size_t)ss.pcount());

Is there an elegant way to format a text message using a concise one-line statement perhaps with templates or macros?

You could check out boost format: http://www.boost.org/doc/libs/1_55_0/libs/format/ — Adrian Cornish, Dec 11 '14 at 01:34
See also: http://stackoverflow.com/questions/2342162/stdstring-formatting-like-sprintf — uncletall, Dec 11 '14 at 01:35
@πάντα ῥεῖ Ugh, that question and its answers are horrible. I wish you hadn't closed this; I was _just_ about to submit a good answer with a good example for _this_ OP's specific question. *Sigh*. Oh well. — Lightness Races in Orbit, Dec 11 '14 at 01:45
Agree it is not a duplicate the way it was asked - Alex obviously wanted something else even though boost format is in that question way down the list — Adrian Cornish, Dec 11 '14 at 01:46
boost format was inspired by python I believe. enven though python 3 dropped the syntax. — v.oddou, Dec 11 '14 at 01:47
If you really want a one-liner, you can do this: `string msg = (ostringstream("Selected elements: ") << i << "," << j << ".").str();` Note the use of `ostringstream` instead of `ostrstream`. — Remy Lebeau, Dec 11 '14 at 01:55
@LightnessRacesinOrbit _"I was just about to submit a good answer with a good example for this OP's specific question."_ ?? — πάντα ῥεῖ, Dec 11 '14 at 02:34
Possible duplicate: http://stackoverflow.com/q/2342162/560648 (but I'm still not convinced) — Lightness Races in Orbit, Dec 11 '14 at 10:12

score 3 · Accepted Answer · answered Dec 11 '14 at 10:10

3

Yes; you are looking for Boost.Format:

const int i = 3, j = 4;
const std::string msg = (boost::format("Selected elements: %d %d") % i % j).str();

(live demo)

answered Dec 11 '14 at 10:10

Lightness Races in Orbit

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dconman · Answer 2 · 2014-12-11T02:33:24.993

-6

What you are most likely looking for is sprintf which works like printf, but returns a cstring. Thus your code would be
string msg(sprintf( "Selected elements: %d, %d.", i, j ) )

EDIT

Looks like I didn't read my own link. So again you have a three line code. You could always define the following

std::string itostr( int i )
{
    char temp[20];
    std::sprintf( temp, "%d" i);
    std::string out(temp);
    return out;
}

Then you can just use the + operator to concat strings.

string msg("Selected elements: " + itostr(i) + "," + itostr(j) + ".");

edited Dec 11 '14 at 02:33

answered Dec 11 '14 at 02:00

dconman

90
3

this cannot work. `sprintf` outputs the result in its first argument. here your first argument is the format string. which should be a constant. – v.oddou Dec 11 '14 at 02:06
_`std::sprintf()`_ is the worst recommendation I can think of here. – πάντα ῥεῖ Dec 11 '14 at 02:37

Preferred method for string formatting in c++?

2 Answers2