The **`perror()` function** displays the description of the error that corresponds to an error code stored in the system variable `errno`.

> **`errno`** is a system variable which holds the error code that describes the error condition. This error condition is produced by a call to a library function.

# Syntax


## Input
- **`str`:** The pointer to a null-terminated string. This string should contain an explanatory message about the error.


# Code
The **`perror()` function** outputs the error description by combining the following in the given order:

- The contents of the string pointed to by `str`.
- The character ":".
- The error message corresponding to the error code in the variable `errno`.

#include <stdio.h>

int main () {
  FILE *fp;

  /* If we try to open a file that does not exist
  the variable errno will be set accordingly. */
  fp = fopen("file.txt", "r");
  if( fp == NULL ) {
    // The following string is prepended to the error description.
    perror("The error is ");
    return(-1);
  }
  fclose(fp); 
  return(0);
}

What is perror() in C++?

The perror() function displays the description of the error that corresponds to an error code stored in the system variable errno.  errno is a system variable which holds the error code that describes the error condition. This error condition is produced by a call to a library function.  Syntax 