指針變量與其指向內(nèi)存的關(guān)系

指針變量也是一種變量，占有內(nèi)存空間，用來保存內(nèi)存地址測試指針變量占有內(nèi)存空間大小。

#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int main0101(){ char* p = NULL; char buf[] = "abcde"; printf("p1=%d\n", p); //改變指針變量的值 p = buf; printf("p2=%d\n", p); //指針變量和它指向的內(nèi)存塊是兩個不同的概念 p = p + 1;//改變指針變量的值，即改變了指針的指向 printf("p3=%d\n", p); printf("buf=%s\n", buf); printf("*p=%c\n", *p);//b printf(" 改變指針指向的內(nèi)存，并不會改變指針的值\n"); buf[1] = '1'; printf("p4=%d\n", p); printf("buf2=%s\n", buf); *p = 'm'; printf("p5=%d\n", p); printf("buf3=%s\n", buf); //寫內(nèi)存時，一定要確保內(nèi)存可寫 //char* buf2 = "aaawwweee";//該字符串在文字常量區(qū) 不可修改 //buf2[2] = '1';//err char buf3[] = "wwweerrr"; buf3[1] = 's';//ok //不允許向NULL和未知非法地址拷貝內(nèi)存。 char* p3 = NULL;//err //char* p3 = 0x1111;//err //給p3指向的內(nèi)存中拷貝字符串 p3 = buf3;//ok strcpy(p3, "123"); return 0;}修改指針變量的結(jié)果#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int main0201(){ char* p = NULL; char* q = NULL; char buf[100] = "asdzcx"; p = &buf[0]; printf("p=%d,%c\n", p,*p); p = &buf[1]; printf("p2=%d,%c\n", p, *p); printf("\n"); for (int i = 0; i < strlen(buf); i++) { p = &buf[i]; printf("p3=%d,%c\n", p, *p); } q = (char*)malloc(100); if (q == NULL) { return -1; } strcpy(q, "qqqwww"); for (int i = 0; i < strlen(q); i++) { p = q + i; printf("%c\n", *p); } return 0;}3.通過指針間接復(fù)賦值#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int get_a(){ int a = 10; return a;}void get_a2(int b){ b = 20;}void get_a3(int* p){ *p = 20;//通過*操作內(nèi)存}void get_a4(int* a1, int* a2, int* a3, int* a4){ *a1 = 1; *a2 = 2; *a3 = 3; *a4 = 4;}int main0301(){ int a = 100; int* p = NULL; //建立關(guān)系 //指針指向誰，就將誰的地址賦值給指針 p = &a; //通過*操作內(nèi)存 *p = 22; /* 通過指針間接賦值 1.兩個變量 2.建立關(guān)系 3.通過*操作內(nèi)存 */ int b = get_a(); printf("b===%d\n", b); get_a2(b); printf("b2===%d\n", b); //如果想通過形參改變實參的值，必須地址傳遞 get_a3(&b);//函數(shù)調(diào)用時建立關(guān)系 printf("b3===%d\n", b); int a1, a2, a3, a4; get_a4(&a1,&a2,&a3,&a4); printf("a1=%d,a2=%d,a3=%d,a4=%d", a1, a2, a3, a4); return 0;}static void fun2(int* p){ p = 0xaabb; printf("fun2:p=%p\n", p);}static void fun3(int** p){ *p = 0xaabb; printf("fun3:p=%p\n", *p);}int main0302(){ //一個變量，應(yīng)該定義一個怎樣類型的指針來保存它的地址 //在原來的基礎(chǔ)上加一個* //int a = 10; //int* p = &a; //int** q = &p; //int********* t = NULL; //int********** t2 = &t; int* p = 0x1122; printf("p1=%p\n", p); fun2(p);//值傳遞 printf("p2=%p\n", p); fun3(&p);//值傳遞 printf("p3=%p\n", p); return 0;}4.指針作為函數(shù)參數(shù)的輸入輸出特性#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int get_a(){ int a = 10; return a;}void get_a2(int b){ b = 20;}void get_a3(int* p){ *p = 20;//通過*操作內(nèi)存}void get_a4(int* a1, int* a2, int* a3, int* a4){ *a1 = 1; *a2 = 2; *a3 = 3; *a4 = 4;}int main0301(){ int a = 100; int* p = NULL; //建立關(guān)系 //指針指向誰，就將誰的地址賦值給指針 p = &a; //通過*操作內(nèi)存 *p = 22; /* 通過指針間接賦值 1.兩個變量 2.建立關(guān)系 3.通過*操作內(nèi)存 */ int b = get_a(); printf("b===%d\n", b); get_a2(b); printf("b2===%d\n", b); //如果想通過形參改變實參的值，必須地址傳遞 get_a3(&b);//函數(shù)調(diào)用時建立關(guān)系 printf("b3===%d\n", b); int a1, a2, a3, a4; get_a4(&a1,&a2,&a3,&a4); printf("a1=%d,a2=%d,a3=%d,a4=%d", a1, a2, a3, a4); return 0;}static void fun2(int* p){ p = 0xaabb; printf("fun2:p=%p\n", p);}static void fun3(int** p){ *p = 0xaabb; printf("fun3:p=%p\n", *p);}int main0302(){ //一個變量，應(yīng)該定義一個怎樣類型的指針來保存它的地址 //在原來的基礎(chǔ)上加一個* //int a = 10; //int* p = &a; //int** q = &p; //int********* t = NULL; //int********** t2 = &t; int* p = 0x1122; printf("p1=%p\n", p); fun2(p);//值傳遞 printf("p2=%p\n", p); fun3(&p);//值傳遞 printf("p3=%p\n", p); return 0;}5.字符串初始化#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>/*C語言沒有字符串類型，而是通過字符數(shù)組模擬C語言字符串以字符'\0'即數(shù)字0結(jié)尾*/int main0501(){ //不指定長度，沒有結(jié)束符0，有多少個元素就有多長 char buf[] = { 'a','b','c' };//3個元素 printf("buf=%s\n", buf);//不加\0的話 末尾亂碼 //指定長度，后面沒有賦值的元素位置，自動補(bǔ)0 char buf1[100]= { 'a','b','c' }; printf("buf2=%s\n", buf1); //所謂元素都賦值為0 char buf3[100] = { 0 }; //char buf4[2] = { '1','2','3' };//err 數(shù)組越界 char buf5[50] = { '1','a','b','0','7' }; printf("buf5=%s\n", buf5); char buf6[50] = { '1','a','b',0,'7' }; printf("buf6=%s\n", buf6);// 1ab char buf7[50] = { '1','a','b','\0','7' }; printf("buf7=%s\n", buf7);// 1ab //使用字符串初始化，常用此類方式 char buf8[] = "qaaasss"; //strlen：測字符串長度，但不包含數(shù)字0與字符'\0' //sizeof：測數(shù)組長度，包含數(shù)字0和字符'\0' printf("strlen=%d,sizeof=%d\n", strlen(buf8), sizeof(buf8));//7 8 char buf9[100] = "qaaasss"; printf("strlen=%d,sizeof=%d\n", strlen(buf9), sizeof(buf9));//7 100 printf("test"); // \012相當(dāng)于\n char str[] = "\0129"; printf("%s\n", str); return 0;}int main0502(){ char buf[] = "aaazzzzssssdddd"; char* p = NULL; //[]方式 for (int i = 0; i < strlen(buf); i++) { printf("%c", buf[i]); } printf("\n"); //指針法 //數(shù)組名字，是數(shù)組首元素地址 p = buf; for (int i = 0; i < strlen(buf); i++) { printf("%c", p[i]); } printf("\n"); for (int i = 0; i < strlen(buf); i++) { printf("%c",*(p+i));//編譯器方式 } printf("\n"); for (int i = 0; i < strlen(buf); i++) { printf("%c", *(buf+i)); } printf("\n"); //buf 和 p完全等價嗎 //p++;//ok //buf++;//err //buf只是一個常量，不可修改 return 0;}6.字符串拷貝#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int main0601(){ char src[] = "qqqqqqqqqq"; char dst[100] = { 0 }; int i = 0; for (; src[i] != 0; i++) { dst[i] = src[i]; } //補(bǔ)齊結(jié)束符 dst[i] = 0; printf("%s", dst); return 0;}void my_strcpy(char* dst, char* src){ int i = 0; for (; *(src+i) != 0; i++) { *(dst+i) = *(src+i);//dst[i]=src[i] } // dst[i] = 0; *(dst + i) = 0;}void my_strcpy2(char* dst, char* src){ while (*src!=0) { *dst = *src; src++; dst++; } *dst = 0;}void my_strcpy3(char* dst, char* src){ //*dst=*src //dst++,src++ //判斷*dst是否為0，為0跳出循環(huán) while (*dst++ = *src++) { NULL;//先執(zhí)行，再自加;先*dst=*src,dst++,src++ }}//成功返回0，失敗返回非零//1.判斷形參指針是否為NULL//2.不要直接使用形參 以防止將形參的指針指向末尾int my_strcpy4(char* dst, char* src){ if (dst == NULL || src == NULL) { return -1; } //使用輔助變量將形參的值接來 char* to = dst; char* from = src; //*dst=*src //dst++,src++ //判斷*dst是否為0，為0跳出循環(huán) while (*from++ = *to++) { NULL;//先執(zhí)行，再自加;先*dst=*src,dst++,src++ } printf("my_strcpy4:dst=%s\n", dst); return 0;}int mai0602n(){ char src[] = "qqqqqqqqqq"; char dst[100] = { 0 }; int ret = 0; ret = my_strcpy4(dst, src); if (ret != 0) { printf("my_strcpy4 err:%d\n", ret); return ret; } printf("%s\n", dst); int i = 0; int n = i++; printf("n=%d,i=%d\n", n, i); return 0;}7.strstr中的while與do-while的模型#define _CRT_SECURE_NO_WARNINGS#include<stdio.h>#include<stdlib.h>#include<string.h>#include<time.h>int main01(){ char* p = "sadzxaaadaszxaaaass---zxaa231312zxaa4";//zxaa int n = 0; do { p = strstr(p, "zxaa"); if (p != NULL) { n++;//累計個數(shù) //重新設(shè)置查找起點 p = p + strlen("zxaa"); } else//若沒有匹配的字符串跳出循環(huán) { break; } } while (*p!=0);//如果沒到結(jié)尾 printf("n=%d\n", n); return 0;}int main02(){ char* p = "sadzxaaadaszxaaaass---zxaa231312zxaa4";//zxaa int n = 0; while ((p = strstr(p, "zxaa")) != NULL) { //能進(jìn)循環(huán)一定有匹配到子串 //重新設(shè)置起點位置 p = p + strlen("zxaa"); n++; if (*p == 0)//如果到結(jié)束符 { break; } } printf("n=%d\n", n); return 0;}int my_strstr(char* p, int* n){ //兩個輔助變量 int i = 0; char* temp = p; while ((temp = strstr(temp, "zxaa")) != NULL) { //能進(jìn)循環(huán)一定有匹配到子串 //重新設(shè)置起點位置 temp = temp + strlen("zxaa"); i++; if (*temp == 0)//如果到結(jié)束符 { break; } } *n = i; return 0;}int main07(){ char* p = "sadzxaaadaszxaaaass---zxaa231312zxaa4";//zxaa int n = 0; int ret = 0; ret = my_strstr(p, &n); if (ret != 0) { return ret; } printf("n=%d\n", n); return 0;}