Appending a new line in a file(log file) in c++

Question

I have a logging functionality and in this I have got log files. Now every time I run the program I want that previously written file should not get deleted and should be ap

Answer 1

Use something like:

#include <fstream>
#include <iostream>
using namespace std;
int main() {
  ofstream out("try.txt", ios::app);
  out << "Hello, world!\n";
  return 0;
}

The ios:app option makes the output get appended to the end of the file instead of deleting its contents.

Answer 2

You want to open the file in "append" mode, so it doesn't delete the previous contents of the file. You do that by specifying ios_base::app when you open the file:

std::ofstream log("logfile.txt", std::ios_base::app | std::ios_base::out);

For example, each time you run this, it will add one more line to the file:

#include <ios>
#include <fstream>

int main(){
    std::ofstream log("logfile.txt", std::ios_base::app | std::ios_base::out);

    log << "line\n";
    return 0;
}

So, the first time you run it, you get

line

The second time:

line
line

and so on.

Answer 3

maybe you need to open the file with the append option. like this:

FILE * pFile;
pFile = fopen ("myfile.txt","a");

or this :

fstream filestr;
filestr.open ("test.txt", fstream::app)