C++ cerr object

❮ iostream objects

int x = 5;
int y = 0;

if(y == 0) {
  cerr << "Division by zero: " << x << " / " << y << "\n";
} else {
  cout << (x / y);
}

Definition and Usage

The cerr object is used to output error messages. It behaves identically to cout but it can be directed to a different destination such as an error log file. cerr and clog always write to the same destination.

For more detailed usage, see the <iostream> cout object.

Unlike cout and clog, cerr is not buffered. A buffered output would store the output temporarily in a variable and not write to the destination until certain conditions are met. Buffered outputs are more efficient because they do fewer write operations on files. cerr is not buffered so that the error messages can be written to a file before the program crashes.

Note: The cerr object is defined in the <iostream> header file.

More Examples

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

int main() {
  int x = 5;
  int y = 0;

  // Set "error.log" as the output file for the error messages
  ofstream log("error.log");
  cerr.rdbuf(log.rdbuf());
  
  // Write an error message
  if(y == 0) {
    cerr << "Division by zero: " << x << " / " << y << "\n";
  } else {
    cout << (x / y);
  }

  // Close the file
  log.close();
  
  return 0;
}

❮ iostream objects