Is `if (pointer)` Enough? A Look at Pointer Evaluation in Conditional Statements

Pointer Evaluation in Conditional Statements

When evaluating a pointer within a conditional statement, you may wonder if the expression if (pointer) is sufficient or if if (pointer != NULL) is necessary.

The Null Pointer Trap

The traditional approach, using if (pointer != NULL), explicitly checks if the pointer is not equal to the null pointer value (NULL). However, this approach relies on the assumption that NULL is defined and has a specific value, which can vary depending on the platform and programming language.

Implicit Boolean Conversion

C 11 introduced a mechanism that simplifies pointer evaluation in conditional statements. The null pointer is implicitly converted to the boolean value false, while non-null pointers are converted to true. This means that the expression if (pointer) is functionally equivalent to if (pointer != NULL) as long as the pointer is not of type std::nullptr_t.

Section on Boolean Conversions

According to the C 11 standard, section on Boolean Conversions:

"A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type bool. A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true."

Conclusion

In C 11 and later, you can safely use if (pointer) instead of if (pointer != NULL) to check if a pointer is not null. However, if you are using std::nullptr_t, you should stick with the explicit comparison if (pointer != nullptr) to ensure correct evaluation.

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