C++ reference: ostream::tellp

ostream::tellp
streampos tellp ( );

ostream

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Get position of the put pointer.
Returns the position of the put pointer. The put pointer determines the next location where to write in the buffer associated to the output stream.

Parameters.

none

Return Value.
The function returns an object of type streampos representing the current position of the put pointer.

Example.

// position of put pointer
#include <fstream>
using namespace std;

int main () {
  long pos;

  ofstream outfile;
  outfile.open ("test.txt");

  outfile.write ("This is an apple",16);
  pos=outfile.tellp();
  outfile.seekp (pos-7);
  outfile.write (" sam",4);

  outfile.close();

  return 0;
}

In this example tellp is used to get the position of the put pointer after the write operation. The pointer is moved 7 characters before to modify the file at that position, so the final content of the file shall be:
This is a sample

Basic template member declaration (basic_ostream<charT,traits>):

typedef traits::pos_type pos_type; pos_type tellp ();

See also.
seekp, istream::tellg, istream::seekg,
ostream class