Creating file names automatically C++

Question

I\'m trying to write a program in C++, which creates some files (.txt) and writes down the result in them. The problem is that an amount of these files is not fixed at the begin

Answer 1

You can get a const char* from an std::string by using the c_str member function.

std::string s = ...;
const char* c = s.c_str();

If you don't want to use std::string (maybe you don't want to do memory allocations) then you can use snprintf to create a formatted string:

#include <cstdio>
...
char buffer[16]; // make sure it's big enough
snprintf(buffer, sizeof(buffer), "file_%d.txt", n);

n here is the number in the filename.

Answer 2

 for(int i=0; i!=n; ++i) {
     //create name
     std::string name="file_" + std::to_string(i) + ".txt"; // C++11 for std::to_string 
     //create file
     std::ofstream file(name);
     //if not C++11 then std::ostream file(name.c_str());
     //then do with file
 }

Answer 3

I use the following code for this, you may find this useful.

std::ofstream ofile;

for(unsigned int n = 0; ; ++ n)
{
    std::string fname = std::string("log") + std::tostring(n) << + std::string(".txt");

    std::ifstream ifile;
    ifile.open(fname.c_str());

    if(ifile.is_open())
    {
    }
    else
    {
        ofile.open(fname.c_str());
        break;
    }

    ifile.close();
}

if(!ofile.is_open())
{
    return -1;
}

ofile.close();

Answer 4

Sample code:

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;

string IntToStr(int n) 
{
    stringstream result;
    result << n;
    return result.str();
}

int main () 
{
    ofstream outFile;
    int Number_of_files=20;
    string filename;


  for (int i=0;i<Number_of_files;i++)
  {
        filename="file_" + IntToStr(i) +".txt";
        cout<< filename << "  \n";

        outFile.open(filename.c_str());
        outFile << filename<<" : Writing this to a file.\n";
        outFile.close();
  }


  return 0;
}

Answer 5

... another way to bulid the filename

#include <sstream>

int n = 3;
std::ostringstream os;
os << "file_" << n << ".txt";

std::string s = os.str();