Equivalent of %02d with std::stringstream?

Question

I want to output an integer to a std::stringstream with the equivalent format of printf's %02d. Is there an easier way to achieve this than:

std::stringstream stream;
stream.setfill('0');
stream.setw(2);
stream << value;

Is it possible to stream some sort of format flags to the stringstream, something like (pseudocode):

stream << flags("%02d") << value;

Shouldn't that be `stream.fill('0')` and `stream.width(2)` ? You are using the name of the manipulators almost like you know the answer to your own question? — CB Bailey, May 15 '10 at 09:34

CB Bailey · Accepted Answer · 2010-05-15T09:36:29.067

You can use the standard manipulators from <iomanip> but there isn't a neat one that does both fill and width at once:

stream << std::setfill('0') << std::setw(2) << value;

It wouldn't be hard to write your own object that when inserted into the stream performed both functions:

stream << myfillandw( '0', 2 ) << value;

E.g.

struct myfillandw
{
    myfillandw( char f, int w )
        : fill(f), width(w) {}

    char fill;
    int width;
};

std::ostream& operator<<( std::ostream& o, const myfillandw& a )
{
    o.fill( a.fill );
    o.width( a.width );
    return o;
}

score 12 · Answer 2 · answered May 15 '10 at 09:29

12

You can use

stream<<setfill('0')<<setw(2)<<value;

answered May 15 '10 at 09:29

hpsMouse

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score 11 · Answer 3 · answered May 15 '10 at 09:29

11

You can't do that much better in standard C++. Alternatively, you can use Boost.Format:

stream << boost::format("%|02|")%value;

answered May 15 '10 at 09:29

Marcelo Cantos

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1

And if you are not using the `stream` for anything else, you don't need it, because `boost::format` already produces a string. – UncleBens May 15 '10 at 09:51
1

I heard you have to pass it to `str(...)` then – Johannes Schaub - litb May 15 '10 at 10:18
Jahonnes you can use std::string myStr = (boost::format("%|02|")%value).str(); – Martin Meeser Mar 06 '13 at 09:01

score 5 · Answer 4 · answered Nov 24 '17 at 18:04

Is it possible to stream some sort of format flags to the stringstream?

Unfortunately the standard library doesn't support passing format specifiers as a string, but you can do this with the fmt library:

std::string result = fmt::format("{:02}", value); // Python syntax

or

std::string result = fmt::sprintf("%02d", value); // printf syntax

You don't even need to construct std::stringstream. The format function will return a string directly.

Disclaimer: I'm the author of the fmt library.

score 0 · Answer 5 · edited Sep 12 '20 at 12:16

0

i think you can use c-lick programing.

you can use snprintf

like this

std::stringstream ss;
 char data[3] = {0};
 snprintf(data,3,"%02d",value);
 ss<<data<<std::endl;

edited Sep 12 '20 at 12:16

Arghya Sadhu

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answered Sep 12 '20 at 11:24

Shangbin Dong

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3

score 0 · Answer 6 · answered May 09 '23 at 08:40

I use such function:

#include <stdio.h>
#include <stdarg.h>
#include <cstdio>

const char * sformat(const char * fmt, ...)
{
    static char buffer[4][512]; // nesting less than 4x, length less then 512
    static int i = -1;
    if(++i > 3) i = 0;
    va_list args;
    va_start(args, fmt);
    std::vsnprintf(buffer[i], 511, fmt, args);
    va_end(args);
    return buffer[i];
}

Equivalent of %02d with std::stringstream?

6 Answers6

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