Any benefit of using assert instead of using a simple "if" ?

Question

Given this code :

#include <stdio.h>
#include <assert.h>

void print_number(int* somePtr) {
  assert (somePtr!=NULL);
  printf ("%d\n",*somePtr);
}

int main ()
{
  int a=1234;
  int * b = NULL;
  int * c = NULL;

  b=&a;

  print_number (c);
  print_number (b);

  return 0;
}

I can do this instead :

#include <stdio.h>
#include <assert.h>

void print_number(int* somePtr) {
  if (somePtr != NULL)
       printf ("%d\n",*somePtr);
  // else do something 
}

int main ()
{
  int a=1234;
  int * b = NULL;
  int * c = NULL;

  b=&a;

  print_number (c);
  print_number (b);

  return 0;
}

So , what am I gaining by using assert ?

Regards

Answer 1

assert is to document your assumptions in the code. if statement is to handle different logical scenarios.

Now in your specific case, think from the point of view of the developer of the print_number() function.

For example when you write

void print_number(int* somePtr) {
  assert (somePtr!=NULL);
  printf ("%d\n",*somePtr);
}

you mean to say that,

In my print_number function I assume that always the pointer coming is not null. I would be very very surprised if this is null. I don't care to handle this scenario at all in my code.

But, if you write

void print_number(int* somePtr) {
  if (somePtr != NULL)
       printf ("%d\n",*somePtr);
  // else do something 
}

You seem to say that, in my print_number function, I expect people to pass a null pointer. And I know how to handle this situation and I do handle this with an else condition.

So, sometimes you will know how to handle certain situations and you want to do that. Then, use if. Sometimes, you assume that something will not happen and you don't care to handle it. You just express your surprise and stop your program execution there with assert.

Answer 2

Lots of reasons:

1. Asserts are usually removed for release builds.
2. Asserts will report failure information to the client. if() does nothing by itself.
3. Because asserts are usually macros, you can also get code information about the failing assertion.
4. Assert is more semantically clear than if().