I was taking a look at the assert() reference page and I got stuck while I read the given example:

/* assert example */
#include <stdio.h>
#include <assert.h>

int main ()
{
  FILE * datafile;
  datafile=fopen ("file.dat","r");
  assert (datafile);

  fclose (datafile);

  return 0;
}

In this example, assert is used to abort the program execution if datafile compares equal to 0, which happens when the previous call to fopen was not successful.

I totally agree that if fopen() fails, assert() will abort execution. However I'm concerned about the rightness of this example:

In my opinion assert() is there to detect cases that can't normally happen (like passing a NULL pointer to a function whose documentation states it is forbidden).

In this example, failing to open a file is not something that can't normally happen. In fact, I can see dozens of reasons why this would fail. The file couldn't exist, the program could run without required privileges, and so on.

I would rather have done something like:

/* not longer an assert example */
#include <stdio.h>
#include <assert.h>

int main ()
{
  FILE * datafile;
  datafile=fopen ("file.dat","r");

  if (datafile != NULL)
  {
    // Do something, whatever.
    fclose (datafile);
  } else
  {
    // Report the error somehow.
  }

  return 0;
}

Is my understanding of how assert() should be used incorrect ?

EDIT AND GOOD NEWS !

It seems the referred site is ruled by rigorous people. Here is the mail I got back from one of the site maintainer:

Hi Julien, I have to agree, the example code was poorly chosen. It has now been just re