Number of digits for an int to use in a file name in c++

Question

I need to use some integer values as a part of some file names I create as outputs in a c++ program. For this I use the code above. The thing is my int values ( named n_irrad in the code) goes from 1 to 20000 for example, so I need the file names to be MC_Interface00001.txt, MC_Interface00002.txt, ..., MC_Interface20000.txt. So, ¿how can I set the number of digits in the file name? With the code I'm using I obviously get MC_Interface1.txt, MC_Interface2.txt, ..., MC_Interface20000.txt.

Thanks in advance.

ofstream MC_Interface;
string Irrad = static_cast<ostringstream*>( &(ostringstream() << n_irrad) )->str();
string MC_Interface_FileName = "MC_Interface" + Irrad + ".txt";
MC_Interface.open(MC_Interface_FileName.c_str());

Use [setw](http://www.cplusplus.com/reference/iomanip/setw/) and [setfill](http://www.cplusplus.com/reference/iomanip/setfill/). — eerorika, Jun 26 '14 at 11:52
Why the casting for the `std::ostringstream` formatting? Doing e.g. `std::string Irrad = (std::ostringstream() << n_irrad).str();` should work just as fine. — Some programmer dude, Jun 26 '14 at 11:52
@Joachim That won’t work, `operator<<` returns an `ostream` which has no `str` member function. I’m not sure why this is a pointer cast though – it should be a reference cast instead. — Konrad Rudolph, Jun 26 '14 at 12:00
@KonradRudolph In that case clang's libc++ contain a bug, because it works fine there. — Some programmer dude, Jun 26 '14 at 12:11
@Konrad If I don't use a pointer it also fails for me. Not sure why really. — Pablo, Jun 26 '14 at 12:20
@Pablo I mean `static_cast(ostringstream() << y).str()` – that definitely works. — Konrad Rudolph, Jun 26 '14 at 12:59
@Konrad It works, sorry. My fault, I was keeping ->str(). Thank you very much. — Pablo, Jun 26 '14 at 13:09

score 1 · Answer 1 · answered Jun 26 '14 at 12:03

Try the following

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

int main() 
{
    std::ostringstream os;

    os << std::setw( 5 ) << std::setfill( '0' ) << 10;

    std::string s = "MC_Interface" + os.str();
    std::cout << s << std::endl;

    return 0;
}

The output is

MC_Interface00010

score 0 · Answer 2 · 2014-06-26T11:59:43.070

0

ofstream MC_Interface;
std::stringstream ss("MC_Interface");
ss << std::setw(5) << std::setfill('0') << n_irrad;
ss << ".txt";
MC_Interface.open(ss.str());

edited Jun 26 '14 at 11:59

answered Jun 26 '14 at 11:53

I missclicked I was editing sorry. – Jun 26 '14 at 11:58

Number of digits for an int to use in a file name in c++

2 Answers2