This rule is part of MISRA C++:2023.
MISRA Rule 7.11.1
Category: Required
Analysis Type: Decidable,Single Translation Unit
Amplification
Using any integral literal representing zero, including the literal 0 or the macro NULL, to represent the
null-pointer-constant is a violation of this rule.
In addition, the macro NULL shall not be used in any other context.
Rationale
The C++ Standard defines the object nullptr as the null-pointer-constant.
The literal 0 can also be used to represent a null-pointer-constant. However, 0 has type int, and
its use can lead to unexpected overload resolution. Note that the macro NULL expands to 0.
Note: some library functions provide overloads for std::nullptr_t so that they can be selected during overload
resolution at compile-time, avoiding the need for a run-time check against nullptr.
Example
void f1( int32_t * );
void f2()
{
f1( nullptr ); // Compliant
f1( 0 ); // Non-compliant - 0 used as the null pointer constant
}
The following example shows the selection of an integer overload when NULL (which has a value of 0) is used instead of
nullptr:
void f3( int32_t );
void f3( int32_t * );
void f4()
{
f3( NULL ); // Non-compliant - calls the int32_t overload
f3( nullptr ); // Compliant - calls the int32_t * overload
}
The following example shows non-compliant uses of NULL, where it is not used as the null-pointer-constant:
#define MYNULL NULL // Non-compliant
void f5()
{
int32_t one = NULL + 1; // Non-compliant - NULL used as an integer
throw NULL; // Non-compliant - caught by catch ( int )
}
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