C语言 结构体作为参数和返回值使用

方案一：结构体变量作为参数，进行传值。

　　　　编译器需要拷贝，不影响origin value，使用成员操作符(.)直接访问

/**********************************************************************
* 版权所有 (C)2017, Wang maochun。
*
* 文件名称：travel.cpp
* 文件标识：无
* 内容摘要：主要演示结构体作为参数以及返回值 
* 其它说明："传值” 
* 当前版本：V1.0
* 作    者：Wang maochun
* 完成日期：2017.7.23
*
**********************************************************************/
#include <iostream>

struct travel_time
{
    int hours;
    int mins;
};

const int Mins_per_hr = 60;

travel_time sum(travel_time t1,travel_time t2);
void show_time(travel_time t);

int main()
{
    using namespace std;
    travel_time day1 = {5,45};  //5 hours 45 minutes
    travel_time day2 = {4,55};  //4 housr 55 minutes
    
    travel_time trip = sum(day1,day2);
    cout << "Two-day total:";
    show_time(trip);
    
    travel_time day3 = {4,32};
    cout << "Three-day total:";
    show_time(sum(trip,day3)); 
    
    return 0;
}

travel_time sum(travel_time t1,travel_time t2)
{
    travel_time total;
    
    total.mins = (t1.mins + t2.mins) % Mins_per_hr;
    total.hours = (t1.hours + t2.hours) + (t1.mins + t2.mins) / Mins_per_hr;
    
    return total;
}

void show_time(travel_time t)
{
    using namespace std;
    cout << t.hours << "hours,"
         << t.mins  << "minutes
";
} 

运行结果：

---

方案二：结构体指针作为参数，传地址。

　　　　编译器不需要拷贝，和main函数采用相同地址。为了不影响origin value，使用const修饰

　　　　使用指针指向结构体操作符(->)间接访问

/**********************************************************************
* 版权所有 (C)2017, Wang maochun。
*
* 文件名称：travel.cpp
* 文件标识：无
* 内容摘要：主要演示结构体作为参数以及返回值 
* 其它说明："传地址” 
* 当前版本：V1.0
* 作    者：Wang maochun
* 完成日期：2017.7.23
*
**********************************************************************/
#include <iostream>

struct travel_time
{
    int hours;
    int mins;
};

const int Mins_per_hr = 60;

travel_time sum(travel_time* t1,travel_time* t2);
void show_time(travel_time* t);

int main()
{
    using namespace std;
    travel_time day1 = {5,45};  //5 hours 45 minutes
    travel_time day2 = {4,55};  //4 housr 55 minutes
    
    travel_time trip = sum(&day1,&day2);
    cout << "Two-day total:";
    show_time(&trip);
    
    travel_time day3 = {4,32};
    cout << "Three-day total:";
    travel_time trip1 =sum(&trip,&day3);
    show_time(&(trip1)); 
    
    return 0;
}

travel_time sum(travel_time* t1,travel_time* t2)
{
    travel_time total;
    
    total.mins = (t1->mins + t2->mins) % Mins_per_hr;
    total.hours = (t1->hours + t2->hours) + (t1->mins + t2->mins) / Mins_per_hr;
    
    return total;
}

void show_time(travel_time* t)
{
    using namespace std;
    cout << t->hours << "hours,"
         << t->mins  << "minutes
";
} 

结果和方案一相同。

出现的错误：

show_time(&(sum(&day1,&day2)));这样写时，出现taking address of temporary fpermissive错误。
原因是：
Your middle result which is a temporary variable since it will disappear
If you assign the result of sum(&day1,&day2) to a variable then it will no longer be a temporary and you can then take the address of it.
因此，不能对未赋值的临时变量取地址