Two pointer to a string

 

// pointer to a character string has not changed successfully 
char str1 [20 is] = "Notepad"; 
char str2 [20 is] = "Calc"; 
void Change (char * str) {// copy mechanism have the function will create a new variable str to store the main function p pass over str1 the first address 
    printf ( "str in change:% p,% p \ the n-", str, str2); // str in change: 00403008,0040301C 
    str = str2; // change New str address pointer variable, and it did not affect the main function of the p address 
    the printf ( "Change:% S,% p \ n-", str, str); // Change: Calc, 0040301C 
} 
void main () { 
    char * p str1 =; 
    printf ( "p in main:% p,% p \ the n-", p, str1); // in main p: 00403008,00403008 
    change (p); // change does not change the point p in 
    printf ( " Change After:% S, P% \ n-", P, P); // After Change: Notepad, 00,403,008 
}

 

//一级指针字符串　　　　改变成功，改变其指向的内容
#include <string.h>
char str1[20] ="notepad";
char str2[20] ="calc";
void change(char *str){       //函数有副本机制，会新建一个变量str来存储main函数中p传过来str1的首地址
    printf("str in change: %p,%p\n",str,str2); //str in change: 00403008,0040301C

    //根据p传过来的地址，用字符数组拷贝的方式，改变主函数中p所指向的字符串
    strcpy(str,str2);  //把str和p共同指向的同一片内存区域的内存修改了，导致主函数也修改了
    printf("change:%s,%p\n",str,str); //change:calc,00403008
}
void main(){
    char *p =str1;
    printf("p in main: %p,%p\n",p,str1);  //p in main: 00403008,00403008
    change(p);  // //把str和p共同指向的同一片内存区域的内存修改了，导致主函数也修改了
    printf("after change: %s,%p\n",p,p);  //after change: calc,00403008
}

 

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//二级指针字符串
#include <string.h>
char str1[20] ="notepad";
char str2[20] ="calc";
void change(char **str){       //函数有副本机制，会新建一个二级指针变量str来存储main函数中p传过来str1的首地址
    printf("str in change: %p,%p\n",str,str2); //str in change: 00403008,0040301C

    *str = str2;  // *str就相当于一级指针 char * 用来改变main中p指针变量自己的首地址  *str=p=str2
    printf("change:%s,%p\n",*str,*str); //change:calc,0040301c
}
void main(){
    char *p =str1;
    printf("p in main: %p,%p\n",p,str1);  //p in main: 00403008,00403008
    change(&p);  //change把p的指向给改变，等价于p=str2
    printf("after change: %s,%p\n",p,p);  //after change: calc,0040301c
}