[英]C++ assignment operator during declaration
這是我的 Hero 類,帶有兩個重載賦值運算符 - Hero to Hero 和 String to Hero。
#include <iostream>
class Hero {
private:
int x;
std::string name;
public:
Hero():x(42), name("JohnDoe") {};
Hero(int a, std::string b):x(a), name(b) {};
void print(){
std::cout<<name<<" : "<<x<<"\n";
}
const Hero &operator =(const Hero &other){
std::cout<<"Overloaded Assignment class to class! \n";
x = other.x;
name = other.name;
return *this;
}
const Hero &operator =(const std::string N){
std::cout<<"Overloaded Assignment from string! \n";
x = 777;
name = N;
return *this;
}
};
int main(){
Hero foo(42, "Hercules");
Hero zak = foo; // Regular assignmnet, not the overloaded
// Hero bar = "HelloWorld"; <<<< Illegal
Hero zoo(HelloWorld",42); << Ok, but here we use constructor, not an assignment operator
Hero bar;
bar = "Ayax"; // "Overloaded Assignment from string! \n";
zak = bar; //"Overloaded Assignment class to class! \n";
zak.print();
bar.print();
}
和產生的結果:
Overloaded Assignment from string!
Overloaded Assignment class to class!
Ayax : 777
Ayax : 777
為什么不能在聲明中使用重載運算符進行變量初始化?
在行中Hero zak = foo;
編譯器使用非重載運算符,字符串Hero bar = "HelloWorld"
是非法的。
在定義時初始化對象時,即使使用=
語法也不使用賦值。
當你這樣做時:
Hero zak = foo;
它相當於:
Hero zak(foo);
這是復制初始化,因此調用復制構造函數。
問題在於
Hero bar = "HelloWorld";
是它等價於:
Hero bar = Hero("HelloWorld");
這又相當於:
Hero bar(Hero("HelloWorld"));
而且由於您沒有Hero("HelloWorld")
的構造函數,所以它是無效的。
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