Integer to clock format - Crash

[ToniAz]

Hello everyone!

I am supposed to test the runtime of some algorithms with diffrent complexities as a function of m. Given some values for m, I need to change m to a "clock" format you know day hr : min : sec : msec.

Here's the code for conversion:

string format(int m)
{
    int ms;
    int ss;
    int mm;
    int dd;
    int hh;
    ms = m%1000;
    m = (m - ms)/1000;
    ss = m%60;
    m = (m - ss)/60;
    mm = m%60;
    m = (m - mm)/60;
    hh = m%24;
    dd = (m - hh)/24;
    char * charr;
    sprintf(charr, "%03d %02d:%02d:%02d:%02d", dd, hh, mm, ss, ms);     
    return charr;
}

Now I'm inputing the runtime in a text file, using the following code:

outData << setw(9)  << "1" << setw(8) <<
               setw(18) << format(log10(1)) <<
               setw(18) << format(sqrt(1)) <<
               setw(9)  << format(1) << setw(8) <<               
               setw(18) << format(1*log10(1)) <<
               setw(18) << format(1*1) <<
               setw(18) << format(1*1*1) <<
               setw(18) << format(2^1) <<
               setw(18) << format(fact(1)) << endl;

But for some reason the program is crashing.
What would be the problem?
Any help is appreciated!

[Duthomhas]

It should have crashed on Windows, also. (You are just lucky that it didn't.)

Line 16 only allocates a pointer variable -- the pointer does not point to anything in particular. The crash likely occurs on line 17 when you try to sprintf() to some random memory location.

I do have to wonder why you are using sprintf() at all. Why not use the C++ way?

#include <iomanip>
#include <sstream>
#include <string> 

string format(int m)
{
    int ms = m%1000;    m /= 1000;
    int ss = m%60;      m /= 60;
    int mm = m%60;      m /= 60;
    int hh = m%24;      m /= 24;
    int dd = m;
    ostringstream result;
    result << setfill( '0' )
           << setw( 3 ) << dd << " "
           << setw( 2 ) << hh << ":"
           << setw( 2 ) << mm << ":"
           << setw( 2 ) << ss << ":"
           << setw( 2 ) << ms;
    return result.str();
}

That said, if you must, change your line 16 to read

  16     char charr[ 17 ];

That will be implicitly-constructed into a string when you return it.

Hope this helps.