const與參考
Prerequisites:
const參考
const參考可以放左值(l-value)，也可以放右值(r-value)，也可以放常數。
const參考放左值
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int main() {
// i 是l-value
int i = 100; // 100 is r-value
const int& ref_i = i;
cout << "ref_i = " << ref_i << endl;
return 0;
}
ref_i = 100
const參考放右值
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int main() {
const int& ref_r = 100; // 100 is r-value
cout << "ref_r = " << ref_i << endl;
return 0;
}
ref_r = 100
const參考放右值&&變數名
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int main() {
int&& r = 100;
const int& ref_r = r;
cout << "ref_r = " << ref_i << endl;
return 0;
}
ref_r = 100
const參考放常數名
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int main() {
//con 是常數
const int con = 100;
const int& ref = con;
cout << "ref = " << ref << endl;
return 0;
}
ref = 100
const參考放常數值
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int main() {
const int& ref = 100; //100是常數
cout << "ref = " << ref << endl;
return 0;
}
ref = 100
函式參數為const參考
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void func(const int& ref) {
cout << "ref = " << ref << endl;
}
int main() {
// i is l-value
int i = 10;
//l-value
func(i);
//r-value
int&& r = 20;
func(r);
func(100);// 常數 100 , 100 is r-value
func('A');// 常數 'A' , A is r-value
return 0;
}
ref = 10
ref = 20
ref = 100
ref = 65