Assert in C Programming

Asserts are used in programs if the developer wishes to assert or make assumptions. An example where we can use assert is to check whether the pointer that is returned by malloc() is a NULL value or not. It is a diagnostic tool.

The Syntax for assert() function in C Programming

It takes an expression for the parameter in the function. The parameter is evaluated. If the value returned after evaluation of the expression is 0 or FALSE, it returns the expression along with the file name and line of execution as an error. If the errors occur, the program calls the abort() function. The assert function does not do anything if the expression is evaluated TRUE.

Implementing assert() in a Program

To implement the assert() function in your program, you must include assert.h header file in your program.

#include <stdio.h>
#include <assert.h> 
int main()
{int constt = 100;
// The portion contains multiple lines of code
// Assuming that some operations have been performed in the code
// that have changed the value of constt from 100 to 10.
constt = 10;
// the programmer is unaware of these changes
// and assumed that the value of constt is still 100.
assert(constt==100);
//code after assertion.
return 0;
}

Output:

In the program below, an assertion is made since the condition is false. The assertions fail.

Assert vs Error Handling in C Programming

The programmer uses assertions to check the logically incorrect conditions. It is used in those scenarios where the programmers want to ensure the state of the code before running or completing the execution of the program. Such situations can't happen logically.

Error handling is performed during the runtime, whereas the asserts statement does not run during the run time. It is advised to not use the assert() statement in your program while execution as it may cause side effects during the execution.

Ignore the Assertions in your Program

As discussed, the assert statement may cause side effects during the compile time of the program and removing all the assertions from the code is a very tedious and difficult process.

In C programming language, there is an easier method that completely removes all the assert statements from your code during the execution.

It is done using the preprocessor NDEBUG.

Below is the code implementing assert while using the NDEBUG.

// The program return below will not through any error because we have //defined the pre-processor NDEBUG in it.
#define NDEBUG
# include <assert.h>
int main()
{
int constant = 10;
assert (constant==1);
return 0;
}

Output: