This rule is part of MISRA C++:2023.
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Rule 11.3.2 - The declaration [1] of an object should contain no more than two levels of pointer indirection
Category: Advisory
Analysis: Decidable,Single Translation Unit
Amplification
Any typedef-name appearing in a declaration [1] is treated as if it were replaced by the type that it denotes.
Note: the pointer decay that occurs when declaring a function parameter of array type introduces a level of pointer
indirection.
Rationale
Use of more than two levels of indirection can seriously impair the ability to understand the behaviour of the code, and therefore should be
avoided.
Example
typedef int8_t * INTPTR1;
using INTPTR2 = int8_t *;
struct s
{
int8_t * s1; // Compliant
int8_t ** s2; // Compliant
int8_t *** s3; // Non-compliant
};
struct s * ps1; // Compliant
struct s ** ps2; // Compliant
struct s *** ps3; // Non-compliant
int8_t ** ( *pfunc1 )(); // Compliant
int8_t ** ( **pfunc2 )(); // Compliant
int8_t ** ( ***pfunc3 )(); // Non-compliant
int8_t *** ( **pfunc4 )(); // Non-compliant
void function( int8_t * par1, // Compliant
int8_t ** par2, // Compliant
int8_t *** par3, // Non-compliant
INTPTR1 * par4, // Compliant
INTPTR1 * const * const par5, // Non-compliant
int8_t * par6[], // Compliant
int8_t ** par7[], // Non-compliant
int8_t ** &par8) // Compliant
{
int8_t * ptr1; // Compliant
int8_t ** ptr2; // Compliant
int8_t *** ptr3; // Non-compliant
INTPTR2 * ptr4; // Compliant
INTPTR2 * const * const ptr5; // Non-compliant
int8_t * ptr6[ 10 ]; // Compliant
int8_t ** ptr7[ 10 ]; // Compliant
}
Explanation of types:
-
par1 and ptr1 are of type pointer to int8_t.
-
par2 and ptr2 are of type pointer to pointer to int8_t.
-
par3 and ptr3 are of type pointer to a pointer to a pointer to int8_t. This is three levels and is
non-compliant.
-
par4 and ptr4 are expanded to a type of pointer to a pointer to int8_t.
-
par5 and ptr5 are expanded to a type of const pointer to a const pointer to a pointer to int8_t. This is
three levels and is non-compliant.
-
par6 is of type pointer to pointer to int8_t because arrays are converted to a pointer to the initial element of the
array.
-
ptr6 is of type array of pointers to int8_t.
-
par7 is of type pointer to pointer to pointer to int8_t because arrays are converted to a pointer to the initial
element of the array. This is three levels and is non-compliant.
-
ptr7 is of type array of pointer to pointer to int8_t. This is compliant.
-
par8 is of type reference to pointer to pointer to int8_t. This is compliant.
Glossary
[1] Declaration
A declaration introduces the name of an entity into a translation unit (see [basic.def]/1).
An entity may be declared several times. The first declaration of an entity in a translation unit is
called an introduction [2]. All subsequent declarations are called redeclarations [3].
A definition [4] is a declaration, as described in [basic.def]/2.
[2] Introduction
See declaration [1].
[3] Redeclaration
See declaration [1].
[4] Definition
See declaration [1].
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