const char and static const char

部分内容摘自：https://blog.csdn.net/ranhui_xia/article/details/32696669

The version with const char * will copy data from a read-only location to a variable on the stack.

The version with static const char * references the data in the read-only location (no copy is performed).

在函数内部，const char *每次调用函数时，都需要在stack上分配内存，然后将数据拷贝过来，函数退出前释放。

而static const char *，会直接访问read only的数据，无需再stack上分配内存。

char * const cp     : 定义一个指向字符的指针常数，即const指针

const char* p       : 定义一个指向字符常数的指针

char const* p       : 等同于const char* p

举个例子：

 #include <iostream>
 #include <cstdio>
 using namespace std;

 int main()
 {
     char ch[] = {'a','b','c'};
     char* const cp = ch;
     printf("char* const cp: \n %c\n", *cp);
     /*
     ** cp point to a fixed address
     **
     cp++;  //error: increment of read-only variable ‘cp’
     printf("char* const cp: \n %c\n", *cp);
     **
     */

     const char ca = 'a';
     const char* p1 = &ca;

     /*
     ** 2. Only const char* pointer can point to a const char
     **
     const char cb = 'b';
     char* p2 = &cb; //error: invalid conversion from ‘const char*’ to ‘char*’
     **
     **/

     /*
     ** 3. p1 points to a const char, the char be pointed has to be const,
     **    p1 can point to a different const char
     */
     printf("const char* p1: \n %c\n", *p1);
     const char cb = 'b';
     p1 = &cb;
     printf(" %c\n", *p1);
     return ;
 }

 /*
 ** Output:
 char* const cp:
  a
 const char* p1:
  a
  b
 **
 */