Is (NULL == bCondition) Better Than (bCondition == NULL) for Null Checks?

Comparing NULL Values: Evaluating (bCondition == NULL) vs. (NULL == bCondition)

In programming, a common task when working with pointers or objects is checking if they are null. There are two common notations for performing this check: (bCondition == NULL) and (NULL == bCondition). While both appear to serve the same purpose, there is a subtle difference in their behavior.

Why Use (NULL == bCondition)?

The primary reason for using (NULL == bCondition) instead of (bCondition == NULL) is to provide increased protection against typos. Specifically, when comparing a variable to NULL, it's possible to accidentally use an assignment operator (=) instead of the comparison operator (==).

For example, consider the following code:

if (bCondition = NULL)  // typo here
{
  // Code never executes
}

In this example, the programmer mistakenly used the assignment operator (=) instead of the comparison operator (==). As a result, bCondition will always be set to NULL, and the code within the if statement will never execute.

By using (NULL == bCondition), a compiler will issue an error or warning if an assignment operator is used, highlighting the potential typo. For instance:

if (NULL = bCondition) // error -> compiler complains
{
  // ...
}

Compiler Behavior and NullPointerExceptions

In some languages, the choice between (bCondition == NULL) and (NULL == bCondition) can also impact the way null pointer exceptions are handled.

In languages where NULL is a constant, using (bCondition == NULL) can result in a NullPointerException if bCondition is not initialized to a valid pointer. On the other hand, using (NULL == bCondition) ensures that an exception will only be thrown if bCondition attempts to access an invalid memory location.

Sample Comparison

To illustrate the difference between (bCondition == NULL) and (NULL == bCondition), consider the following example:

int *p = NULL;

if (p == NULL)
{
  // Execute this block if p is null
}

if (NULL == p)
{
  // Execute this block if p is null
}

In this example, both if statements will execute the same code. However, if the assignment operator (=) was accidentally used in the first statement, it would result in a compiler warning or error.

Conclusion

While (bCondition == NULL) and (NULL == bCondition) may seem interchangeable at first glance, using (NULL == bCondition) provides additional protection against accidental typos and can improve the handling of null pointer exceptions. As a general rule, it is recommended to use (NULL == bCondition) when checking for null values.

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