creating and reading/writing to files with fstream in C++

Question

I'm looking to create a file, then open it and rewrite to it.

I've found I can create a file by simply doing this:

#include <iostream>
#include <fstream>  
using namespace std;
int main()
{
ofstream outfile ("test.txt");
outfile << "my text here!" << endl;
outfile.close();
return 0;
}

while this works to create the test file, I cannot open the file and then edit it. this (below) does not work even after the file is created.

outfile.open("test.txt", ios::out);
if (outfile.is_open())
{
    outfile << "write this to the file";
}
else
    cout << "File could not be opened";
outfile.close;

Answer 1

If by "does not work" you mean that the text is overwritten instead of appended, you need to specify std::ios::app as one of the flags to the call to open to have it append more data instead of overwriting everything.

outfile.open("test.txt", ios::out | ios::app);

The following example works fine for me:

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
  ofstream outfile ("test.txt");
  outfile << "my text here!" << endl;
  outfile.close();

  outfile.open("test.txt", ios::out | ios::app );
  if (outfile.is_open())
     outfile << "write this to the file" << endl;
  else
     cout << "File could not be opened";

  outfile.close();

  return 0;
}

Produces the following text file:

my text here!
write this to the file

Answer 2

You can also do that with FOPEN. Some compilers will notice you that the function its OBSOLETE or DEPRECATED but for me its working good.

/* fopen example */
#include <stdio.h>
int main ()
{
  FILE * pFile;
  pFile = fopen ("myfile.txt","w");
  if (pFile!=NULL)
  {
    fputs ("fopen example",pFile);
    fclose (pFile);
  }
  return 0;
}

More info here: http://www.cplusplus.com/reference/cstdio/fopen/