C 语言指针的用法

1.指针基本介绍

 

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

int main() {

    int a = 10;
    int *pa = &a;
    printf("%d\n", *pa);

    int32_t *intP = (int32_t *) malloc(4);
    *intP = 100;
    printf("%d\n", *intP);

    int32_t *intPo = (int32_t *) malloc(4);
    intPo[0] = 101;
    printf("%d\n", *intPo);

    int len = 10;
    int32_t *intPoi = (int32_t *) malloc(len * sizeof(int32_t));
    intPoi[0] = 102;
    intPoi[1] = 103;
    printf("%d\n", intPoi[1]);
    printf("%d\n", *(intPoi + 1));
    free(intPoi);

    char *str = "Hello";
    printf("%ld\n", sizeof(str));//指针长度 64位 8  32位 4
    int64_t poin = (int64_t) str;//int64_t和指针相互转换  JNI(Java Native Interface) Java long==C int64_t
    char *str1 = (char *) poin;
    printf("%s\n", str1);
    return 0;
}

 

2.函数指针

 

#include <stdio.h>

void hello(){
    printf("Hello World!\n");
}

//自定义
typedef void (*SimpleFunc)();

int main() {

    //常规方式
    hello();

    //函数指针
    void (*fp)() = &hello;
    fp();

    //自定义
    SimpleFunc simpleFunc = &hello;
    simpleFunc();
    return 0;
}

 

3.无类型指针

 

#include <stdio.h>
#include <stdlib.h>

int main() {

    //无类型指针
    void *data = "Hello C";
    printf("%s\n", data);

    void *a = malloc(8);
    printf("%ld\n", sizeof(a[0]));//无类型指针的访问单元  1字节

    void *b = malloc(8);
    int *intb = b;
    printf("%ld\n", sizeof(intb[0]));//指定类型后 变成4字节

    intb[0] = 10000;
    printf("%d\n", intb[0]);
    free(b);

    void *c = 10000;
    printf("%d\n", c);

    return 0;
}