The `perror()` function displays the description of the error that corresponds to the error code stored in the system variable `errno`.
>**`errno`** is a system variable that holds the error code referring to the error condition. A call to a library function produces this error condition.

# Syntax


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

# Code
The `perror()` function shows the output in the following order:
- The contents of the string pointed to by specified pointer i.e., `str`
- Followed by ":"
- Then appends the ﻿error message corresponding to the error code in variable `errno`

#include <stdio.h>


int main() 
{
  FILE *fp;
  //First Rename The Existing File
  rename("file.txt" , "newfile.txt");

  //Now try to open file with old name
  fp = fopen ( "file.txt" , "r");
  if ( fp == NULL)
  {
    perror("Error!!!");
    return (-1);
  }
  fclose(fp);
  return 0;
}

What is perror in C?

Displays the error description for the code in errno, prefixed with a custom message.