Dutor

char ** a;
const char ** b;
char * const * c;
const char * const * d;
const char * const * const e;

#include <iostream>
#include <string>
 
using namespace std;
 
void test1(){
    char **s; //s是数组的指针;
    s = NULL;
    s = new char*[4];
    for (int i = 0; i < 4; ++i){
        s[i] = new char[10];
        strcpy(s[i], "test");
    }
    for (int i = 0; i < 4; ++i){
        printf("%s\n", s[i]);
    }
    for (int i = 0; i < 4; ++i){
        delete[] s[i];
    }
    delete[] s;
}
 
void test2(){
    const char **s; //s是指向字符串常量的指针
    s = NULL;
    char b[4][10] = {"a","b","c","d"};
    s = new const char*[4];
    for (int i = 0; i < 4; ++i){
        s[i] = b[i]; // OK
        //s[i][0] = 'd'; //这句要报错,因为s[i]指向的是字符串常量
                    //即使b[i]字符串本不是常量(编译期间添加的属性)
    }
    for (int i = 0; i < 4; ++i){
        printf("%s\n", s[i]);
    }
    delete[] s;
}
 
void test3(){
    char * const * s; //s指向常量数组，数组的每一个元素是字符指针常量。
                //数组的元素不可改，但数组元素指向的字符串可修改    
    s = NULL;// s不是常量
    char a[4][10] = {"aa", "bb", "cc", "dd"};
    char * const(b[4]) = {a[0], a[1], a[2], a[3]};
    s = b;
    for (int i = 0; i < 4; ++i){
        s[i][1] = 'd'; //OK
        //s[i] = NULL; //报错，因为s[i]是常量
        printf("%s\n", s[i]);
    }
}
 
void test4(){
    const char * const * s; //s指向一个常量指针数组
    //数组的每一个元素是字符指针常量，指向字符串常量(绕口令阿这是。。。)
    s = NULL;// s不是常量
    char a[4][10] = {"aa", "bb", "cc", "dd"};
    char * const(b[4]) = {a[0], a[1], a[2], a[3]};
    s = b;
    for (int i = 0; i < 4; ++i){
        //s[i][1] = 'd'; //报错，因为s[i][j]是常量
        //s[i] = NULL; //报错，因为s[i]是常量
        printf("%s\n", s[i]);
    }
}
 
void test5(){
    char a[4][10] = {"aa", "bb", "cc", "dd"};
    const char * const(b[4]) = {a[0], a[1], a[2], a[3]};
    const char * const * const s = b;
    //s是一个常量指针，指向一个常量指针数组
    //数组的每一个元素是字符指针常量，指向字符串常量(这才是绕口令！)
    //s = NULL; //Error, s是常量
    for (int i = 0; i < 4; ++i){
        //s[i][1] = 'd'; //报错，因为s[i][j]是常量
        //s[i] = NULL; //报错，因为s[i]是常量
        printf("%s\n", s[i]);
    }
}
 
int main(){
    test1();
	test2();
	test3();
	test4();
	test5();
    return 0;
}