C/C++ 关于结构体变量传参时遇到的问题

阐述

主函数中的结构体变量作为非主函数的参数时,若只是将结构体变量名传与非主函数, 那就意味着仅是将其值传递给了非主函数内部,相当于在非主函数内部复制粘贴了一个新的结构体(此处称之为X),这个新结构体X与主函数中的结构体(此处称之为Y)是相互独立的,但它们二者的初始成员值都相同.

struct SSS{
    ...
};

void NonMain(SSS X){
    // X & Y的初始成员值都相同, 地址却相异
    ...
}

int main(){
    SSS Y;
    NonMain(Y);
    return 0;
}

根据上述代码,如果在NonMain函数中改变了结构体变量内部的值,当NonMain函数运行结束后,程序返回主函数时,主函数中原有的结构体变量内部不会有丝毫变化.
这是因为结构体变量名本身不是地址, 非主函数内所操作的结构体变量的地址,并非主函数中的结构体变量的地址.

因此,正确的结构体变量传参与非主函数时,需要先取出结构体变量的地址当作指针,再将指针传与非主函数.

代码示例

#include <string>
#include <cstring>
#include <iostream>
#include <queue>
using namespace std;

typedef struct TimesRecord
{
        int year;
        int month;
        int day;
} times;

void initializationError(TimesRecord date_record)
{
        date_record.year = 2015;
        date_record.month = 5;
        date_record.day = 18;

        cout << "initializationError.&date_record: " << &date_record << endl;
}

void alterError(TimesRecord date_record, int newYear, int newMonth, int newDay)
{
        date_record.year = newYear;
        date_record.month = newMonth;
        date_record.day = newDay;
        cout << "alterError.&date_record: " << &date_record << endl;
}

/* ----------------------------------------------------------------------------- */

void initializationCorrect(TimesRecord &date_record)
{
        date_record.year = 2015;
        date_record.month = 5;
        date_record.day = 18;
        cout << "initializationCorrect.&date_record: " << &date_record << endl;
}

void alterCorrect(TimesRecord &date_record, int newYear, int newMonth, int newDay)
{
        date_record.year = newYear;
        date_record.month = newMonth;
        date_record.day = newDay;
        cout << "alterCorrect.&date_record: " << &date_record << endl;
}

int main(int argc, char const *argv[])
{
        TimesRecord t;
        int newYear = 2006;
        int newMonth = 9;
        int newDay = 22;

        initializationError(t);
        cout << "Error initialization: ";
        cout << t.year << "-" << t.month << "-" << t.day << endl;
        cout << "main.&t: " << &t << endl;

        cout << endl;

        alterError(t, newYear, newMonth, newDay);
        cout << "Error Alter: ";
        cout << t.year << "-" << t.month << "-" << t.day << endl;
        cout << "main.&t: " << &t << endl;

        cout << endl;

        initializationCorrect(t);
        cout << "Correct initialization: ";
        cout << t.year << "-" << t.month << "-" << t.day << endl;
        cout << "main.&t: " << &t << endl;

        cout << endl;

        alterCorrect(t, newYear, newMonth, newDay);
        cout << "Correct Alter: ";
        cout << t.year << "-" << t.month << "-" << t.day << endl;
        cout << "main.&t: " << &t << endl;

        return 0;
}

---

运行结果

initializationError.&date_record: 0x7ffc498004b0
Error initialization: -5234528-22046-1233126896
main.&t: 0x7ffc498004e8

alterError.&date_record: 0x7ffc498004b0
Error Alter: -5234528-22046-1233126896
main.&t: 0x7ffc498004e8

initializationCorrect.&date_record: 0x7ffc498004e8
Correct initialization: 2015-5-18
main.&t: 0x7ffc498004e8

alterCorrect.&date_record: 0x7ffc498004e8
Correct Alter: 2006-9-22
main.&t: 0x7ffc498004e8