Perror() in C
When we create C programs, we frequently run into situations when things fail to continue as expected. It might be a result of user input system problems or other unexpected factors. In such situations, handling mistakes sincerely is critical rather than allowing the program to crash or act unpredictably. In this article, we will discuss about the Perror() function in C with their syntax and usage.
What is Perror()?
The Perror()function in C is a built-in error management function. It is used to send an error message to the standard error stream (stderr), which is different from the standard output stream (stdout).
The Perror() function takes a string argument which is the error message to be printed. After that, it appends to it a description of the system error that occurred based on the value of the global variable "errno". The "errno" variable is set by system calls and other library functions when they encounter errors.
Using Perror() can help programmers quickly identify the cause of errors during program execution. It can also help users understand why a program failed to execute as expected by providing clear and informative error messages.
Perror() is a simple yet effective function that helps improve the reliability and usability of C programs. It is frequently used in combination with other error-handling approaches like error code exception handling and debugging tools.
Syntax and usage of Perror() function in C:
The Perror() function is part of the header file <stdio.h> which provides standard input and output functions in C. Its syntax is as follows:
Code
void perror(const char *str);
The function only takes a pointer to a string (const char *str) as its single argument. The custom error message is provided by the programmer, which is the basis for this argument and is typically used to identify the error's context or source. A colon and a space separate the string and the error message before they are printed.
The Perror() function automatically adds a description of the system error to the error message that is based on the value of the global variable "errno". This variable is set by framework calls and other library capabilities when they experience errors.
The Perror() capability prints the error message to the standard error stream (stderr), which is a different result channel from the standard result stream (stdout). Error messages can now be distinguished from regular program output by being displayed separately from them.
Error handling with Perror() function in C
Error handling is an essential programming component because it enables programs to handle unexpected errors that may occur during program execution gracefully. The Perror() function is a useful error-handling tool in C programming because it can quickly identify and diagnose errors and provide users with helpful error messages.
The Perror() function is often used in conjunction with other error-handling methods like error code handlingexceptions and debugging tools. When a mistake happens, the program can utilize the Perror() capability to print a custom error message to the standard mistake stream (stderr) alongside a description of the error that happened.
Let's take an example program that reads information from a file. The program can use the Perror() function to print an error message and a description of the error if the file does not exist. This message will indicate that the file could not be opened.
Here is an example of how to handle errors with the Perror() function in C:
Code
#include <stdio.h> #include <errno.h> int main() { FILE *fp = fopen("non_existent_file.txt", "r"); if (fp == NULL) { perror("Error opening file"); return errno; } //Read data from the file fclose(fp); return 0; }
Output:
Error opening file: Invalid file or directory
Explanation:
Using the fopen() function, the program tries to open a file that does not exist in this example. The program uses the Perror () function to print an error message indicating that the file cannot be opened if the opening attempt fails. The system calls the error code and then returns it by the program as the value of the errno variable.
By utilizing the Perror() function, the program can give the client a reasonable mistake message showing the error's source and nature. It can assist the client with understanding the reason why the program neglected to execute true to form and make a proper move to determine the issue.
Examples of using the Perror() function in C programming:
In C programming, the perror() function is used to print descriptive error messages to the standard error stream (stderr). It can be particularly helpful in handling error conditions and providing meaningful feedback to the user. Let's take some examples to explain how perror() function works.
Example 1:
Code
#include <stdio.h> #include <errno.h> int main() { FILE *file = fopen("nonexistentfile.txt", "r"); if (file == NULL) { perror("Error"); } return 0; }
We are trying to read a file called "nonexistentfile.txt" in this example. Because the file does not exist, fopen() will fail and return a NULL pointer. To display an error message explaining the reason for the failure call perror("Error").
Output:
Error: Invalid file or directory
Based on the value of the global variable errno, the perror() function produces the proper error message after adding a colon (:) to the given error message. In this situation, fopen() sets the errno value to reflect a "No such file or directory" error.
Example 2:
Code
#include <stdio.h> #include <errno.h> int main() { FILE *file = fopen("file.txt", "r"); if (file == NULL) { perror("Error"); printf("Error opening file: %s\n", strerror(errno)); } else { // File opened successfully fclose(file); } return 0; }
In this example, we try to open a file named "file.txt" for reading once more. However, the file is present this time. If no problems occur, the fopen() function returns a non-NULL pointer, and the file is successfully opened.
Output:
Error: Permission denied Error opening file: Permission denied
Explanation:
In this situation, the fopen() method fails because of a "Permission denied" error. The perror() method returns a detailed error message, while the strerror(errno) function returns the same message. It allows us to display additional information or handle the error condition as required.