Put C++ Const Type Qualifier After the Type
Table of Contents
Best Pratice: Put const type qualifier at the right side of a type you want to decorate.
int var: // var is an int
int const var: // var is a const int
int * ptr; // ptr is a pointer to an int
int const * ptr; // ptr is a pointer to a const int
int * const ptr; // prt is a const pointer to an int
int const * const ptr; // ptr is a const pointer to const an int
int ** ptr; // ptr is a pointer to a pointer to an int
int const ** ptr; // ptr is a pointer to a pointer to a const int
int * const * ptr; // ptr is a pointer to a const pointer to an int
int ** const ptr; // ptr is a const pointer to a pointer to an int
int const * const * const ptr; // ptr is a const pointer to a const pointer to const an int
C++’s const type qualifier first applys to the left of it [1]. If [1] has none, then it decorates the right side [2].
[1] const [2]
The followings means the same thing:
int const var:
const int var: // same meaning
But if you want to apply const to a pointer, it gets complicated.
const int * ptr; // decorates right: ptr is a pointer to a const int
int const * ptr: // decorates left: ptr is a pointer to an const int
int * const ptr: // decorates left: ptr is a const pointer to an int
Of cource, these correctly work. But it looks ugly if there are both styles in your source code.
The simple solution is to apply const to the only right side of a type, which means use only [1] style.
If you have a clear coding rule, your code is easier to understand, even when written in complex syntax like this.
int const ** const ptr; // ptr is a const pointer to a pointer to a const int
Note: When you contribute open source projects or company’s code, it’s better to follow the writing style of existing code and the coding rules of the project.
Reference: