c语言之函数指针的一系列测试

1.先从一个简单的求和求积函数开始

#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;
}

输出：

a_count is 12

m_count is 35

Program ended with exit code: 0

2.试一下函数指针

#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);//声明函数指针
    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;
}

结果不变

a_count is 12

m_count is 35

Program ended with exit code: 0

3.简化一下函数指针的定义

#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);//定义类型fun是一个指向函数的指针
    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;
}

结果不变

a_count is 12

m_count is 35

Program ended with exit code: 0

4.尝试使用一下函数指针数组

#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};//定义函数指针数组

    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;
}

结果不变

a_count is 12

m_count is 35

Program ended with exit code: 0

5.改善函数指针数组

毕竟，函数多了之后，谁能记住乘法是在数组里第几个，下标该是多少。

#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};//定义函数指针数组
    enum func_tpye{ ADD , MUL };  //顺序与上面保持一致

    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;
}

结果不变

a_count is 12

m_count is 35

Program ended with exit code: 0

6.在函数中调不同的函数

之前的例子，直接用函数会更好用一些

#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};//定义函数指针数组
    enum func_tpye{ ADD , MUL };  //顺序与上面保持一致

    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;
}

结果不变

a_count is 12

m_count is 35

Program ended with exit code: 0

7.上面那个例子还可以再扩展的更强大一些

比如说把两个数相乘相加改为多个数相乘相加

#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};//定义函数指针数组
    enum func_tpye{ ADD , MUL };  //顺序与上面保持一致

    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;
}

第一个参数为功能函数，第二个参数为运算的个数，之后是不定参数。

结果为：

a_count is 15

a_count is 16

m_count is 120

m_count is 126

Program ended with exit code: 0