const char *p，char *const p和const char * const p之间的区别 _constchar*constp

先决条件：指针
当char, const, *, p都用在不同的排列中时, 含义会根据放置在何处而变化, 这会引起很多混乱。下一篇文章重点介绍所有这些的区别和用法。
预选赛const可以应用于任何变量的声明以指定其值不会更改。 const关键字适用于左侧的任何内容。如果左侧没有任何内容, 则适用于右侧的任何内容。
const char * ptr：
这是指向常量字符的指针。
你不能更改ptr所指向的值, 但是可以更改指针本身。 ” const char *” 是指向const char的(非const)指针。

//C program to illustrate //char const *p #include< stdio.h> #include< stdlib.h> int main() { char a = 'A' , b = 'B' ; const char *ptr = & a; //*ptr = b; illegal statement (assignment of read-only location *ptr)//ptr can be changed printf ( "value pointed to by ptr: %c\n" , *ptr); ptr = & b; printf ( "value pointed to by ptr: %c\n" , *ptr); }

输出如下：

value pointed to by ptr:A value pointed to by ptr:B

注意：两者之间没有区别const char * p和char const * p因为两者都是指向const char的指针, 并且’ *'(asterik)的位置也相同。
char * const ptr：这是指向非恒定字符的恒定指针。你不能更改指针p, 但可以更改ptr指向的值。

//C program to illustrate //char* const p #include< stdio.h> #include< stdlib.h> int main() { char a = 'A' , b = 'B' ; char * const ptr = & a; printf ( "Value pointed to by ptr: %c\n" , *ptr); printf ( "Address ptr is pointing to: %d\n\n" , ptr); //ptr = & b; illegal statement (assignment of read-only variable ptr)//changing the value at the address ptr is pointing to *ptr = b; printf ( "Value pointed to by ptr: %c\n" , *ptr); printf ( "Address ptr is pointing to: %d\n" , ptr); }

【const char *p，char *const p和const char * const p之间的区别】输出如下：

Value pointed to by ptr: A Address ptr is pointing to: -1443150762Value pointed to by ptr: B Address ptr is pointing to: -1443150762

注意：指针始终指向相同的地址, 仅更改该位置的值。
const char * const ptr：这是指向常量字符的常量指针。你既不能更改ptr所指向的值, 也不能更改指针ptr。

//C program to illustrate //const char * const ptr #include< stdio.h> #include< stdlib.h> int main() { char a = 'A' , b = 'B' ; const char * const ptr = & a; printf ( "Value pointed to by ptr: %c\n" , *ptr); printf ( "Address ptr is pointing to: %d\n\n" , ptr); //ptr = & b; illegal statement (assignment of read-only variable ptr) //*ptr = b; illegal statement (assignment of read-only location *ptr)}

输出如下：