C语言学习-17-函数作为参数传入函数

一、开场白

我们经常需要计算某个函数的时间，定位一下到底是哪个函数跑得慢，所以就想以此为例，介绍一下函数如何作为参数传入到函数当中。

二、代码

#include <stdio.h>
#include <time.h>

unsigned long Recursion(unsigned long Num);
void ComputeProcedureTime(unsigned long(*Func)(unsigned long), unsigned long Num);

int main()
{
    
    unsigned long TempNum = 12;
    ComputeProcedureTime(Recursion, TempNum);

    return 0;
}

void ComputeProcedureTime(unsigned long (*Func)(unsigned long), unsigned long Num)
{
    
    printf("++++++++++++++++++++++++\n");
    clock_t start, finish;
    clock_t Total_time;
    start = clock();

    printf("%lu\n", Func(Num));

    finish = clock();
    Total_time = finish - start;
    printf("Elapsed Time : %ld ms\n", Total_time);
}

unsigned long Recursion(unsigned long Num)
{
    
    if (Num == 1)
    {
    
        return Num;
    }
    else
    {
    
        return Recursion(Num - 1) * Num;
    }
}

三、小口诀

函数作为参数到底怎么写嘞：
（1）我们先把需要传入的函数写上void ComputeProcedureTime(unsigned long Recursion(unsigned long Num), unsigned long Num)。

（2）把unsigned long Recursion(unsigned long Num)的函数名变为(*你想要的名字)。

（3）再把后面的参数名Num去掉。

（4）大功告成，变为了void ComputeProcedureTime(unsigned long (*Func)(unsigned long), unsigned long Num)

四、运行结果

C:\Users\czg> C:\Users\czg\source\repos\x64\Debug\C_TEST.exe
++++++++++++++++++++++++
479001600
Elapsed Time : 1 ms