指针笔试

一 .指针笔试讲解

二. 回调函数

本节内容如下

一.指针笔试讲解

#include <stdio.h>
int Add(int x, int y)
{
  return x + y;
}
int main()
{
  int (*p)(int, int) = Add;
  int sum = (*p)(1, 2);
  printf("%d\n", sum);
  return 0;
}

#include<stdio.h>
int main()
{
  int a[] = { 1,2,3,4 };
  printf("%d\n", sizeof(a));
  printf("%d\n", sizeof(a+0));
  printf("%d\n", sizeof(*a));
  printf("%d\n", sizeof(a+1));
  printf("%d\n", sizeof(a[1]));
  printf("%d\n", sizeof(&a));
  printf("%d\n", sizeof(*&a));
  printf("%d\n", sizeof(&a[0]+1));
  printf("%d\n", sizeof(&a[0]+1));
  return 0;
}

char arr[] = { 'a','b','c','d','e','f', };
  printf("%d\n", sizeof(arr));
  printf("%d\n", sizeof(arr+0));
  printf("%d\n", sizeof(*arr)); 
  printf("%d\n", sizeof(arr[1]));
  printf("%d\n", sizeof(&arr));
  printf("%d\n", sizeof(&arr+1));
  printf("%d\n", sizeof(&arr[0] + 1));
  printf("%d\n", strlen(arr));
  printf("%d\n", strlen(arr + 0));
//  printf("%d\n", strlen(*arr));
  //printf("%d\n", strlen(arr[1]));
  printf("%d\n", strlen(&arr));
  printf("%d\n", strlen(&arr + 1));
  printf("%d\n", strlen(&arr[0] + 1));
  return 0;
}

char* p = "abcdef";
  printf("%d\n", strlen(p));
  printf("%d\n", strlen(p+1));
  //printf("%d\n", strlen(*p));
  //printf("%d\n", strlen(p[0]));
  printf("%d\n", strlen(&p)); 
  printf("%d\n", strlen(&p+1));
  printf("%d\n", strlen(&p[0]+1));

  printf("%d\n", sizeof(p));
  printf("%d\n", sizeof(p + 1));
  printf("%d\n", sizeof(*p));
  printf("%d\n", sizeof(p[0]));
  printf("%d\n", sizeof(&p));
  printf("%d\n", sizeof(&p + 1));
  printf("%d\n", sizeof(&p[0] + 1));

char arr[] = "abcdef";
  printf("%d\n", strlen(arr));
  printf("%d\n", strlen(arr+0));
  //printf("%d\n", strlen(*arr));
  //printf("%d\n", strlen(arr[1]));
  printf("%d\n", strlen(&arr));
  printf("%d\n", strlen(&arr+1));
  printf("%d\n", strlen(&arr[0]+1));

  printf("%d\n", sizeof(arr));
  printf("%d\n", sizeof(arr+0));
  printf("%d\n", sizeof(*arr));
  printf("%d\n", sizeof(arr[1]));
  printf("%d\n", sizeof(&arr));
  printf("%d\n", sizeof(&arr+1));
  printf("%d\n", sizeof(&arr[0]+1));

int main()
{
  int a[5] = { 1,2,3,4,5 };
  int* pr = (int*)(&a + 1);
  printf("%d %d", *(a + 1), *(pr - 1));
  return 0;
}

#include<stdio.h>
  int main()
  {
    int a[5] = { 1,2,3,4,5 };
    int* pa1 = (int*)(&a + 1);
    int* pa2 = (int*)((int)a + 1);
    printf("%x %x", pa1[-1], *pa2);
    return 0;
  }

int main()
{
  int aa[2][5] = { 1,2,3,4,5,6,7,8,9,10 };
  int* pa1 = (int*)(&aa + 1);
  int* pa2 = (int*)(*(aa + 1));
  printf("%d,%d", *(pa1 - 1), *(pa2 - 1));
  return 0;
}

​一般情况下数组名是首元素地址。​

​有例外情况​

​1.sizeof（数组名）表示整个数组​

​2.&数组名 表示整个数组​

二.回调函数：通过函数指针调用的函数叫做回调函数。

qsort函数可以用来排序任意类型的数据，（库函数）。

表达式；
void sqort(void *base,size-t num,size-t width,
int (*cmp)(const void*e1,const void*e2));
//void*类型的指针，可以接受任意类型的地址

int char_cmp(const void* e1, const void* e2)
{
  assert(e1&& e2);

  //因为数组里存的是字符串的地址，所以要强制类型转换成(char **)
  //然后再解引用一下才是字符串的地址
  return strcmp(*(char**)e1, *(char**)e2);
  
}

指针完结