[C++] 變量、指針、引用作函數參數的區別
來源：程序員人生 發布時間：2014-12-12 08:03:44 閱讀次數：3299次
//============================================================================
// Name : CppLab.cpp
// Author : sodino
// Version :
// Copyright : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================
#include <iostream>
#include <string>
using namespace std;
struct Student{
string name;
};
int main() {
void print(Student);
void print_point(Student *);
void print_reference(Student &);
struct Student stu = {"Yao ming"};
cout << "main &stu=" << &stu << endl << endl;
print(stu);
cout << "after print() name=" << stu.name << " no changed."<< endl << endl;
print_point(&stu);
cout << "after print_point() name=" << stu.name << " has been modified." << endl << endl;
print_reference(stu);
cout << "after print_reference() name=" << stu.name << " has been modified." << endl;
return 0;
}
void print(Student stu) {
// 實參轉形參，會消耗額外的時間。print_reference()則效力高許多。
cout << "print() stu address=" << &stu << " is different."<< endl; // 形參stu與函數體外的stu是兩個不同的對象！！
stu.name = "new.name"; // 這里的賦值其實不會改變函數體外stu的name
cout << "print() set new name=" << stu.name << endl;
}
void print_point(Student * stu) {
stu->name = "new.point.name";
cout << "print_point() set new name=" << stu->name << endl;
}
void print_reference(Student &stu) {
stu.name = "new.reference.name";
cout << "set new name=" << stu.name << endl;
}
main &stu=0x7fff5eabfbc8
print() stu address=0x7fff5eabfba0 is different.
print() set new name=new.name
after print() name=Yao ming no changed.
print_point() set new name=new.point.name
after print_point() name=new.point.name has been modified.
set new name=new.reference.name
after print_reference() name=new.reference.name has been modified.
print():用結構體變量作為實參和形參，簡單明了，但在調用函數時
形參要額外開辟內存，實參中全部內容通過值傳遞逐一傳給形參。造成空間和時間上的浪費。
print_point():指定亦是作為實參和形參，實參只是將stu的起始地址傳給形參，而不是逐一傳遞，也沒有額外的內存開辟，效力高。但可讀性可能不是很好。
print_reference():實參是結構體Student類型變量，而形參用該類型的援用，在履行函數期間，函數體操作的stu是函數體外的stu，可讀性亦強。
C++中增設援用變量，提高效力的同時保持了高可讀性。
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