How to convert an integer to a string with a fixed number of digits in c++?

Question

For examples, with 4 digits, convert 0 to "0000"; and 12 to "0012".

Any good way in c++?

Sorry not making it clear, my compiler doesn't support snprintf, and I want a function like

std::string ToString(int value, int digitsCount);

<sstream> provides that sort of formatting capability, as does ye olde sprintf. — Qaz
– Qaz, Commented Dec 17, 2012 at 21:00
@H2CO3, Indeed. I don't use it, so I guess I could lie and argue I was talking about the base of that set of functions. — Qaz
– Qaz, Commented Dec 17, 2012 at 21:04

mohaps · Accepted Answer · 2012-12-17 21:03:04Z

5

char buf[5];
snprintf(buf, sizeof(buf), "%04d", intVal);

edited Dec 17, 2012 at 21:03

user529758

answered Dec 17, 2012 at 21:00

mohaps

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7 Comments

user529758 Over a year ago

No, please, don't sprintf()! If you use this function family, use the secure version!

user529758 Over a year ago

@Caribou That's not a problem, the printf() family of functions works just fine in C++, but really, the secure variations should be used.

mohaps Over a year ago

@H2CO3, I'm using sprintf on a static char buffer allocated on the stack with a length specified by me. so given all of this, sprintf() is secure enough. I posted the snprintf() version if that's more preferable :)

Caribou Over a year ago

@H2CO3 I suppose it is probably a reasonable lightweight way of outputting what the OP wants - streams just come to me more readily these days....

user529758 Over a year ago

@Caribou the problem with sprintf is that one day you WILL eventually change your buffer from static to mallocated one, you also will change its size, etc. So it IS insecure. Because we're humans and we make mistakes. Why not prevent them? Adding an 'n' should not hurt.

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Nikanos Polykarpou · Accepted Answer · 2012-12-17 21:14:19Z

3

Maybe something like this

#include <iostream>
#include <iomanip>
#include <sstream>

using namespace std;

string ToString(int value,int digitsCount)
{
    ostringstream os;
    os<<setfill('0')<<setw(digitsCount)<<value;
    return os.str();
}

int main()
{
    cout<<ToString(0,4)<<endl;
    cout<<ToString(12,4)<<endl;
}

answered Dec 17, 2012 at 21:14

Nikanos Polykarpou

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