黑马程序员—C学习笔记—指针字符串与其内存细节

本节是个人学习过程中的笔记，供初学者一起学习，欢迎大家批评指正，留言参与讨论，谢谢。
本节涉及到指针字符串和数组字符串的存储等基本问题，涉及很多细节，详细变化请参考代码，谢谢。

#include <stdio.h>
#include <string.h>

int main()
{
char name[]="Jack";
char* name1="Jack";
char* name2="Jack";
char* name3="Jack\0";
char name4[]="Jack\0";

char n1[]={'J','a','c','k'};
char n2[]={'J','a','c','k','\0'};
//    char* n3={'J','a','c','k'};这两种做法应该是错误的，指针字符串应该指向字符常量，而右侧字符数组的值是可以改变的
//    char* n4={'J','a','c','k','\0'};

//如何把'\0'作为最后一个字符输入数组中呢？放在中间啥效果？
char n5[]={'J','a','\0','k','\0'};
char n6[]={'J','a','\0','c','k'};

printf("name:%s\n",name);  //这5行都输出 jack
printf("name1:%s\n",name1);
printf("name2:%s\n",name2);
printf("name3:%s\n",name3);//默认都不输出\0
printf("name4:%s\n",name4);

printf("n1:%s\n",n1);//输出jackjack ==》n1的定义方法有错，需要写出最后一个\0 否则容易出错
printf("n2:%s\n",n2); //输出jack
//printf("n3:%s\n",n3);输出错误，程序中断
//printf("n4:%s\n",n4);输出错误，程序中断
printf("n5:%s\n",n5); //这两行输出ja  ==》遇到\0就停止输出，printf函数中的%s机制类似strlen函数，都是遇到\0为判断标准
printf("n6:%s\n",n6);
//    printf("name:%s\n",name[]);  //这两行错误，不符合语法
//    printf("name1:%s\n",name1[]);

printf("sizeof(name)=%zd\n",sizeof(name)); //输出5, jack四个字符+'\0'，输出的是name数组所占空间为5个字节
printf("sizeof(name1)=%zd\n",sizeof(name1));//输出8,name1为指针变量，所占空间为8个字节，如何输出这个字符串所占空间，即为5呢？？
printf("sizeof(name2)=%zd\n",sizeof(name2));//8
printf("sizeof(name3)=%zd\n",sizeof(name3));//8
printf("sizeof(name4)=%zd\n",sizeof(name4));//6

printf("sizeof(\"Jack\")=%zd\n",sizeof("Jack"));//5

printf("sizeof(n1)=%zd\n",sizeof(n1));//4
printf("sizeof(n2)=%zd\n",sizeof(n2));//5
//    printf("sizeof(n3)=%zd\n",sizeof(n3));
//    printf("sizeof(n4)=%zd\n",sizeof(n4));
printf("sizeof(n5)=%zd\n",sizeof(n5));//5
printf("sizeof(n6)=%zd\n",sizeof(n6));//5

//sizeof()函数，如果是指针类型就输出8，其他只看元素个数说话，不管\0与否，只有char name[]="Jack";这种情况才默认加一个\0，计算成5.

printf("strlen(name)=%zd\n",strlen(name)); //字符串长度，表示元素个数，'\0'不是有效原酸，所以输出都是4，
printf("strlen(name1)=%zd\n",strlen(name1));//这四个都是4
printf("strlen(name2)=%zd\n",strlen(name2));
printf("strlen(name3)=%zd\n",strlen(name3));
printf("strlen(name4)=%zd\n",strlen(name4));

printf("strlen(n1)=%zd\n",strlen(n1));//8
printf("strlen(n2)=%zd\n",strlen(n2));//4
//printf("strlen(n3)=%zd\n",strlen(n3));
//printf("strlen(n4)=%zd\n",strlen(n4));
printf("strlen(n5)=%zd\n",strlen(n5));//2
printf("strlen(n6)=%zd\n",strlen(n6));//2

printf("name[1]=%c\n",name[1]);//四个都是a
printf("name[1]=%c\n",*(name+1));

printf("name1[1]=%c\n",name1[1]);
printf("name1[1]=%c\n",*(name1+1));

printf("address of name = %p\n",name);
printf("address of name1 = %p\n",name1);//name1 name2地址相同
printf("address of name2 = %p\n",name2);// ==》指针字符串，字符串是常量放在静态内存中
printf("address of name3 = %p\n",name3);
printf("address of name4 = %p\n",name4);

printf("address of n1 = %p\n",n1);
printf("address of n2 = %p\n",n2);
//    printf("address of n3 = %p\n",n3);  //n3 n4 都输出地址0x4a，应该是报错
//    printf("address of n4 = %p\n",n4);
printf("address of n5 = %p\n",n5);
printf("address of n6 = %p\n",n6);

printf("address of \"Jack\" = %p\n",&"jack");//两个jack地址相同，与指针字符串地址又不同。
printf("address of \"Jack\" = %p\n",&"jack");//有无指针指向的字符串常量，也是有区别的。
printf("address of \"Jack\\0\" = %p\n",&"jack\0");

}