Different meanings of different const locations

Const & pointer

In the type declaration, const is used to modify a constant. There are two ways to write it. So, what are the following statements that use const to limit immutable content?

1) const is in front

Const int nvalue; // nvalue is const

Const char * Pcontent; // * Pcontent is const, and Pcontent is variable

Const (char *) Pcontent; // Pcontent is const, * Pcontent is variable

Char * const Pcontent; // Pcontent is const, * Pcontent is variable

Const char * const Pcontent; // both Pcontent and * Pcontent are const

2) const is behind and equal to the above statement

Int const nvalue; // nvalue is const

Char const * Pcontent; // * Pcontent is const, and Pcontent is variable

(Char *) const Pcontent; // Pcontent is const, * Pcontent is variable

Char * const Pcontent; // Pcontent is const, * Pcontent is variable

Char const * const Pcontent; // both Pcontent and * Pcontent are const

Answer and analysis:

Using const and pointer together is a common confusion in C language. In actual development, especially when looking at othersCodeIn this case, it is difficult to judge the author's intention. The following describes my judgment principles:

(This rule is wrong.) (because of the appearance of "()", this rule is sometimes invalid .) Draw a line along the number *. If the const is on the left side of *, the const is used to modify the variable pointed to by the pointer, that is, the pointer points to a constant. If the const is on the right side, const is to modify the pointer itself, that is, the pointer itself is a constant. You can view the actual meaning of the above statement based on this rule, and I believe it will be clear at a glance.

In addition, NOTE: For const (char *), because char * is a whole, equivalent to a type (such as char), the pointer is limited to const.