C语言入门课程学习笔记9：指针

第41课 - 指针：一种特殊的变量

实验-指针的使用

#include <stdio.h>int main()
{int var = 0;int another = 0;int* pVar = NULL;printf("1. var = %d\n", var);printf("1. pVar = %p\n", pVar);pVar = &var;  // 使用指针保存变量的地址*pVar = 100;  // *pVar 等价于 var ， var = 100;printf("2. var = %d\n", var);printf("2. pVar = %p\n", pVar);pVar = &another;  // 改变了 pVar 的指向，使得 pVar 保存 another 的地址*pVar = 1000;     // another = 1000;printf("3. another = %d\n", another);printf("3. pVar = %p\n", pVar);printf("4. add ==> %d\n", var + another + *pVar);   // 100 + 1000 + 1000  ==> 2100return 0;
}
/*
1. var = 0
1. pVar = 0000000000000000
2. var = 100
2. pVar = 000000000061FE14
3. another = 1000
3. pVar = 000000000061FE10
4. add ==> 2100
*/

小结

第42课 - 深入理解指针与地址

实验-指针的类型

#include <stdio.h>int main()
{int i = 10;float f = 10;int* pi = &f;    // WARNING  int* 指向了floatfloat* pf = &f;  // OKprintf("pi = %p, pf = %p\n", pi, pf);printf("*pi = %d, *pf = %f\n", *pi, *pf);pi = i;   // WARNING  *pi = 110;  // OOPSprintf("pi = %p, *pi = %d\n", pi, *pi);return 0;
}

实验

#include <stdio.h>int calculate(int n, long long* pa, long long* pm)
{int ret = 1;if( (1 <= n) && (n <= 20) ){int i = 0;*pa = 0;*pm = 1;for(i=1; i<=n; i++)//  0+1+...+n{			//1*1*...*n*pa = *pa + i;*pm = *pm * i;}}else{ret = 0;}return ret;
}int main()
{long long ar = 0;long long mr = 0;if( calculate(5, &ar, &mr) )printf("ar = %lld, mr = %lld\n", ar, mr);//15   1*2*3*4*5=120return 0;
}

实验

#include <stdio.h>void func(int* p)
{*p = 100;   // 修改内存中 4 字节的数据，即：修改一个整型变量的值
}void swap(int* pa, int* pb)//通过指针交换变量
{int t = 0;t = *pa;*pa = *pb;*pb = t;
}int main()
{int var = 0;int a = 1, b = 2;printf("1. var = %d\n", var);func( &var );printf("2. var = %d\n", var);//100printf("3. a = %d, b = %d\n", a, b);swap(&a, &b);printf("4. a = %d, b = %d\n", a, b);return 0;
}

小结

第43课 - 指针与数组（上）

实验

#include <stdio.h>int main()
{int a[] = {1, 2, 3, 4, 0};int* p = a;  // a 的类型为 int*, &a[0] ==> int*int (*pa) [5] = &a;//指向数组的指针  注意指针类型printf("%p, %p\n", p, a);p++;//p+1==== p+1*sizeof(p)*p = 100;  // a[1] = 100;printf("%d, %d\n", *p, a[1]);printf("%p, %p\n", &a, a);//????值一样 但是意思不一样，数组的地址  数组首元素的地址p = pa;   // WARNING  !!!!   warning: assignment to 'int *' from incompatible pointer type 'int (*)[5]' p = a;while( *p ){printf("%d\n", *p);p++;}return 0;
}
/*
000000000061FDF0, 000000000061FDF0
100, 100
000000000061FDF0, 000000000061FDF0
1
100
3
4
*/

小结

第44课 - 指针与数组（下）

实验

#include <stdio.h>int main()
{int a[] = {1, 2, 3, 4, 5};int* p = a;int i = 0;// a[i] <==> *(a+i) <==> *(p+i) <==> p[i]for(i=0; i<5; i++){printf("%d, %d\n", a[i], *(a + i));}for(i=0; i<5; i++){printf("%d, %d\n", a[i], p[i]);}for(i=0; i<5; i++){printf("%d, %d\n", p[i], *(p + i));}printf("a = %p, p = %p\n", a, p);//值相同printf("&a = %p, &p = %p\n", &a, &p);//值不同return 0;
}

实验

#include <stdio.h>int main()
{int a[] = {1, 2, 3};int* p = a;int v = *p++;//int v=*p,p++;char* s = NULL;printf("%p\n", "D.T.Software");printf("%p\n", "D.T.Software");printf("v = %d, *p = %d\n", v, *p);printf("First = %c\n", *"D.T.Software");s = "D.T.Software";while( *s ) printf("%c", *s++);printf("\n");return 0;
}
/*
0000000000404000
0000000000404000
v = 1, *p = 2
First = D
D.T.Software
*/

小结

第45课 - 指针与函数

实验

#include <stdio.h>int add(int a, int b)
{return a + b;
}int mul(int a, int b)
{return a * b;
}int calculate(int a[], int len, int(*cal)(int, int))
{int ret = a[0];int i = 0;for(i=1; i<len; i++){ret = cal(ret, a[i]);}return ret;
}int main()
{int a[] = {1, 2, 3, 4, 5};int (*pFunc) (int, int) = NULL;pFunc = add;printf("%d\n", pFunc(1, 2));//3printf("%d\n", (*pFunc)(3, 4));//7pFunc = &mul;printf("%d\n", pFunc(5, 6));//30printf("%d\n", (*pFunc)(7, 8));//56printf("1 + ... + 5 = %d\n", calculate(a, 5, add));//15printf("1 * ... * 5 = %d\n", calculate(a, 5, mul));//120return 0;
}

实验

#include <stdio.h>int demo(int arr[], int len)  // int demo(int* arr, int len)//数组求和
{int ret = 0;int i = 0;printf("demo: sizeof(arr) = %d\n", sizeof(arr));// 8 退化为指针了while( i < len ){ret += *arr++;i++;}return ret;
}int main()
{int a[] = {1, 2, 3, 4, 5};// int v = *a++;printf("return value: %d\n", demo(a, 5));//return 0;
}

小结

第46课 - 指针与堆空间

实验

#include <stdio.h>int main()
{char c = 0;int i = 0;float f = 2.0f;double d = 3.0;void* p = NULL;double* pd = NULL;int* pi = NULL;/* void* 指针可以保存任意类型的地址 */p = &c;p = &i;p = &f;p = &d;printf("%p\n", p);// void* 类型的指针无法访问内存中的数据// printf("%f\n", *p);/* void* 类型的变量可以直接合法的赋值给其他具体数据类型的指针变量 */pd = p;pi = p;// void* 是例外，其他指针类型的变量不能相互赋值// pd = pi;return 0;
}

实验

#include <stdio.h>
#include <stdlib.h>int main()
{int* p = malloc(4); // 从堆空间申请 4 个字节当作 int 类型的变量使用if( p != NULL )  // 如果申请失败 p 为 0 ，即：空值{*p = 100;printf("%d\n", *p);//100free(p);}p = malloc(4 * sizeof(int));if( p != NULL ){int i = 0;for(i=0; i<4; i++){p[i] = i * 10;}for(i=0; i<4; i++){printf("%d\n", p[i]);}free(p);}return 0;
}
/*
100
0
10
20
30
*/

小结

第47课 - 指针专题经典问题剖析

 #include <stdio.h>
#include <stdlib.h>int main()
{int a = 0;int b = 1;int* p = &a;  //p指向aint** pp = &p;//pp指向p**pp = 2;   // a = 2;*pp = &b;   // p = &b;  *p = 3;     // b = 3;printf("a = %d, b = %d\n", a, b);return 0;
}

#include <stdio.h>
#include <stdlib.h>int main()
{int a[] = {1, 2, 3, 4};int* pa = a;int b[2][2] = {{1, 2}, {3, 4}};// int** pb = b;  // b 的类型绝对不是 int**  warning: initialization of 'int **' from incompatible pointer type 'int (*)[2]'int (*pnb) [2] = b;  // b 的类型是 int(*)[2]printf("a = %p, pa = %p\n", a, pa);// printf("b = %p, pb = %p\n", b, pb);printf("b = %p, pnb = %p\n", b, pnb);return 0;
}
/*
a = 000000000061FE00, pa = 000000000061FE00
b = 000000000061FDF0, pnb = 000000000061FDF0
*/

#include <stdio.h>
#include <stdlib.h>int getDouble(double** pp, unsigned n)
{int ret = 0;double* pd = malloc(sizeof(double) * n);if( pd != NULL ){printf("pd = %p\n", pd);*pp = pd;ret = 1;}return ret;
}int main()
{double* p = NULL;if( getDouble(&p, 5) ){printf("p = %p\n", p);free(p);}return 0;
}
/*
pd = 00000000006E5CB0
p = 00000000006E5CB0
*/

#include <stdio.h>
#include <stdlib.h>int main()
{int b[2][2] = {{1, 2}, {3, 4}};int (*pnb) [2] = b;  // b 的类型是 int(*)[2]*pnb[0] = 10;//*(pnb[0])*pnb[1] = 30;printf("b[0][0] = %d\n", b[0][0]);printf("b[0][1] = %d\n", b[0][1]);//30printf("b[1][0] = %d\n", b[1][0]);printf("b[1][1] = %d\n", b[1][1]);return 0;
}
/*
b[0][0] = 10
b[0][1] = 2
b[1][0] = 30
b[1][1] = 4
*/

#include <stdio.h>
#include <stdlib.h>int main()
{int b[2][2] = {{1, 2}, {3, 4}};int (*pnb) [2] = b;  // b 的类型是 int(*)[2]*pnb[0] = 10;
int * k=pnb[0] +1;//??  pnb[0] +sizeof(*pnb[0])对了 *k= 20;//  *pnb[1] = 30;
printf("sizeof(pnb) = %d\n", sizeof(pnb));
printf("sizeof(pnb[0]) = %d\n", sizeof(pnb[0]));
printf("sizeof(*pnb) = %d\n", sizeof(*pnb));
printf("sizeof(*pnb[0]) = %d\n", sizeof(*pnb[0]));
printf("pnb=%p\n",pnb);
printf("pnb[0]=%p\n",pnb[0]);
printf("pnb[0]+1=%p\n",pnb[0]+1);printf("sizeof(b) = %d\n", sizeof(b));
printf("sizeof(int[2]) = %d\n", sizeof(int[2]));printf("b[0][0] = %d\n", b[0][0]);printf("b[0][1] = %d\n", b[0][1]);//30printf("b[1][0] = %d\n", b[1][0]);printf("b[1][1] = %d\n", b[1][1]);return 0;
}
/*
sizeof(pnb) = 8
sizeof(pnb[0]) = 8
sizeof(*pnb) = 8
sizeof(*pnb[0]) = 4
pnb=000000000061FE00
pnb[0]=000000000061FE00
pnb[0]+1=000000000061FE04
sizeof(b) = 16
sizeof(int[2]) = 8
b[0][0] = 10
b[0][1] = 20
b[1][0] = 3
b[1][1] = 4
*/

#include <stdio.h>
#include <stdlib.h>int* func()
{int var = 100;return &var;
}int main()
{int* p = func();  // OOPS!!!!// p 指向了不合法的地址，这个地址处没有变量存在// p 是一个野指针，保存不合法地址的指针都是野指针printf("*p = %d\n", *p);*p = 200;   // 改变 func 函数中局部变量 var 的值，是不是非常奇怪？？？printf("*p = %d\n", *p);return 0;
}

小结