爲什麼通過引用更好？

Question

可能重複：
Is it better in C++ to pass by value or pass by constant reference?

看到這些2程序。

bool isShorter(const string s1, const string s2); 

int main() 
{ 
    string s1 = "abc"; 
    string s2 = "abcd"; 
    cout << isShorter(s1,s2); 
} 

bool isShorter(const string s1, const string s2) 
{ 
    return s1.size() < s2.size(); 
} 

和

bool isShorter(const string &s1, const string &s2); 

int main() 
{ 
    string s1 = "abc"; 
    string s2 = "abcd"; 
    cout << isShorter(s1,s2); 
} 

bool isShorter(const string &s1, const string &s2) 
{ 
    return s1.size() < s2.size(); 
} 

爲什麼第二個是更好？

Answer 1

我建議如果你真的有興趣在某些情況下，按值傳遞時，可能會更好，你可能希望看到你讀這SO Question - Is it better in C++ to pass by value or pass by constant reference?

Answer 2

因爲它不必複製字符串。

Answer 3

this.