c語言之函數指標的一系列測試，函數指標一系列

c語言之函數指標的一系列測試，函數指標一系列
1.先從一個簡單的求和求積函數開始

#include <stdio.h>int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int main(){    int a_count = add(5,7);    int m_count = mul(5,7);    printf("a_count is %d\n",a_count);    printf("m_count is %d\n",m_count);        return 0;}

輸出：

a_count is 12

m_count is 35

Program ended with exit code: 0

2.試一下函數指標

#include <stdio.h>int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int main(){    int (*p_add)(int,int);//聲明函數指標    p_add = add;    int (*p_mul)(int,int);    p_mul = mul;        int a_count = p_add(5,7);    int m_count = p_mul(5,7);    printf("a_count is %d\n",a_count);    printf("m_count is %d\n",m_count);        return 0;}

結果不變

a_count is 12

m_count is 35

Program ended with exit code: 0

3.簡化一下函數指標的定義

#include <stdio.h>int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int main(){    typedef int (*fun)(int,int);//定義類型fun是一個指向函數的指標    fun p_add = add;    fun p_mul = mul;        int a_count = p_add(5,7);    int m_count = p_mul(5,7);    printf("a_count is %d\n",a_count);    printf("m_count is %d\n",m_count);        return 0;}

結果不變

a_count is 12

m_count is 35

Program ended with exit code: 0

4.嘗試使用一下函數指標數組

#include <stdio.h>int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int main(){    int (*func[])(int,int) = {add,mul};//定義函數指標數組        int a_count = func[0](5,7);    int m_count = func[1](5,7);    printf("a_count is %d\n",a_count);    printf("m_count is %d\n",m_count);        return 0;}

結果不變

a_count is 12

m_count is 35

Program ended with exit code: 0

5.改善函數指標數組

畢竟，函數多了之後，誰能記住乘法是在數組裡第幾個，下標該是多少。

#include <stdio.h>int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int main(){    int (*func[])(int,int) = {add,mul};//定義函數指標數組    enum func_tpye{ ADD , MUL };  //順序與上面保持一致        int a_count = func[ADD](5,7);    int m_count = func[MUL](5,7);        printf("a_count is %d\n",a_count);    printf("m_count is %d\n",m_count);        return 0;}

結果不變 

a_count is 12

m_count is 35

Program ended with exit code: 0

6.在函數中調不同的函數

之前的例子，直接用函數會更好用一些

#include <stdio.h>typedef  int (*fun)(int,int);int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int add_mul(fun f,int a,int b){    return f(a,b);}int main(){    int (*func[])(int,int) = {add,mul};//定義函數指標數組    enum func_tpye{ ADD , MUL };  //順序與上面保持一致        printf("a_count is %d\n",add_mul(func[ADD], 5, 7));    printf("m_count is %d\n",add_mul(func[MUL], 5, 7));    return 0;}

結果不變

a_count is 12

m_count is 35

Program ended with exit code: 0

7.上面那個例子還可以再擴充的更強大一些

比如說把兩個數相乘相加改為多個數相乘相加

#include <stdio.h>#include <stdarg.h>typedef  int (*fun)(int,int);int add(int a , int b){    return a + b;}int mul(int a , int b){    return a * b;}int add_mul(fun f,int n,...){    va_list ap;    va_start(ap,n);    int count = va_arg(ap, int);    for (int i = 0; i<(n-1); ++i) {        count = f(count,va_arg(ap, int));    }    return count;}int main(){    int (*func[])(int,int) = {add,mul};//定義函數指標數組    enum func_tpye{ ADD , MUL };  //順序與上面保持一致        printf("a_count is %d\n",add_mul(func[ADD], 5,1,2,3,4,5));    printf("a_count is %d\n",add_mul(func[ADD], 3,7,3,6));        printf("m_count is %d\n",add_mul(func[MUL], 5,1,2,3,4,5));    printf("m_count is %d\n",add_mul(func[MUL], 3,7,3,6));    return 0;}

第一個參數為功能函數，第二個參數為運算的個數，之後是不定參數。

結果為：

a_count is 15

a_count is 16

m_count is 120

m_count is 126

Program ended with exit code: 0

C語言怎讓一個函數返回指標

這種方式叫做“用指標函數*creat（）的傳回值來傳遞動態記憶體”，這是一個C文法

首先你要注意，子函數*creat（）用了malloc動態申請記憶體，而return返回的是指標變數所指向的地址，而不是指標！相當於將你所申請的動態記憶體返回給主函數

int *fun(void)//這裡是指標函數
{
int *p = (int *) malloc (int);//動態申請記憶體//p在這裡指向了一塊合法記憶體的地址
return p;
}

void main(void)
{
int *q = NULL;
q = fun();//fun()返回指標p所指向的地址，（指標p是在棧上建立的，所以*fun()函數運行完，指標所分配的記憶體被系統自動釋放）這時q指向p，得到了malloc所申請到的記憶體
free(q);//釋放動態記憶體
}
 
C語言怎聲明一個返回函數指標的函數？

typedef int (*AA)();
AA function();