error_handling.md

Error Handling

A lot of C function calls return a -1 or NULL in case of an error, so quick test on these return values are easily done with for instance an ‘if statement’.

Global Variable errno:

When a function is called in C, a variable named as errno is automatically assigned a code (value) which can be used to identify the type of error that has been encountered. Its a global variable indicating the error occurred during any function call and defined in the header file errno.h.

Below is a list of few different errno values and its corresponding meaning:

errno value	Error
1	Operation not permitted
2	No such file or directory
3	No such process
4	Interrupted system call
5	I/O error
6	No such device or address
7	Argument list too long
8	Exec format error
9	Bad file number
10	No child processes
11	Try again
12	Out of memory
13	Permission denied

Example:

FILE *fp; 
fp = fopen("file.txt ", "r"); 
printf("Value of errno: %d\n ", errno); 

strerror() returns a pointer to the textual representation of the current errno value:

printf("The error message is : %s\n", strerror(errno)); 

perror: It displays the string you pass to it, followed by a colon, a space, and then the textual representation of the current errno value.

perror("Message from perror");

code

Related: exception handling, return,abort,exit