C++ 传递指针给函数 - C++ 基础教程 - 简单教程，简单编程

C++ 允许传递指针给函数，只需要简单地声明函数参数为指针类型即可

void tm_now(unsigned long *ptr_sec)
{
   // 获取当前的秒数
   *ptr_sec = time( NULL );
   return;
}

我们写一个范例演示下如何使用这个 tm_now() 函数

/**
 * file: main.cpp
 * author: 简单教程(www.twle.cn)
 *
 * Copyright © 2015-2065 www.twle.cn. All rights reserved.
 */

#include <iostream>
#include <ctime>

void tm_now(unsigned long *ptr_sec)
{
    // 获取当前的秒数
    *ptr_sec = time( NULL );

    std::cout << "timestamp of now is: " << *ptr_sec;
    std::cout << std::endl;

    return;
}


int main ()
{
    unsigned long sec;

    tm_now( &sec );

   // 输出实际值
   std::cout << "timestamp in sec is :" << sec << std::endl;
   return 0;
}

编译和运行以上范例，输出结果如下

timestamp of now is: 1523415802
timestamp in sec is :1523415802

指针形参 vs 数组形参

能接受指针作为参数的函数，也能接受数组作为参数

/**
 * file: main.cpp
 * author: 简单教程(www.twle.cn)
 *
 * Copyright © 2015-2065 www.twle.cn. All rights reserved.
 */

#include <iostream>

double avg(double *arr, int size) {
    double sum = 0;

    for ( int i = 0; i < size; i++ )
    {
        sum += arr[i];
    }

    return (double)sum/size;
}


int main ()
{

    // 带有 5 个元素的浮点型数组

    double some_num[5] = {1024.0, 512.0, 3, 218, 1171};
    double avg_num;

    // 传递一个指向数组的指针作为参数
    avg_num = avg( some_num,5 ) ;

    // 输出返回值
    std::cout << "avg of some_num is:" << avg_num << std::endl; 

    return 0;
}

编译和运行以上范例，输出结果如下

avg of some_num is:585.6