C Tutorials
| Error Handling in C |
The C programming language provides perror() and strerror() functions which can be used to display the text message associated with errno.
The perror() function displays the string you pass to it, followed by a colon, a space, and then the textual representation of the current errno value.
The strerror() function, which returns a pointer to the textual representation of the current errno value.
Let's try to simulate an error condition and try to open a file which does not exist. Here I'm using both the functions to show the usage, but you can use one or more ways of printing your errors. Second important point to note is that you should use stderr file stream to output all the errors.
#include <stdio.h>
#include <errno.h>
#include <string.h>
extern int errno ;
int main ()
{
FILE * pf;
int errnum;
pf = fopen ("unexist.txt", "rb");
if (pf == NULL)
{
errnum = errno;
fprintf(stderr, "Value of errno: %d\n", errno);
perror("Error printed by perror");
fprintf(stderr, "Error opening file: %s\n", strerror( errnum ));
}
else
{
fclose (pf);
}
return 0;
| Divide by zero error |
It is a common problem that at the time of dividing any number, programmers do not check if a divisor is zero and finally it creates a runtime error.
The code below fixes this by checking if the divisor is zero before dividing:
#include <stdio.h>
#include <stdlib.h>
main()
{
int dividend = 20;
int divisor = 0;
int quotient;
if( divisor == 0){
fprintf(stderr, "Division by zero! Exiting...\n");
exit(-1);
}
quotient = dividend / divisor;
fprintf(stderr, "Value of quotient : %d\n", quotient );
exit(0);
}
| Program Exit Status |
It is a common practice to exit with a value of EXIT_SUCCESS in case of programming is coming out after a successful operation. Here EXIT_SUCCESS is a macro and it is defined as 0.
If you have an error condition in your program and you are coming out then you should exit with a status EXIT_FAILURE which is defined as -1. So let's write above program as follows:
#include <stdio.h>
#include <stdlib.h>
main()
{
int dividend = 20;
int divisor = 5;
int quotient;
if( divisor == 0){
fprintf(stderr, "Division by zero! Exiting...\n");
exit(EXIT_FAILURE);
}
quotient = dividend / divisor;
fprintf(stderr, "Value of quotient : %d\n", quotient );
exit(EXIT_SUCCESS);
}
|
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