对象的初始化

三个方法

direct initialization c++98

• 依赖 = 或 ()
• 适用于built in typed
• 如 int foo=2.0 缺点：导致 narrowing conversion :编译器隐式转换

uniform initialization (C++11)

• 使用于所有类型 包括自己定义的
• consistent type-safe
• using {}
• 按顺序

strutured binding c++17

• initialing variables from data structure with size known at compile-time

std::tuple<std::string,std::string,std::string> getclassinfo(){
    std::string classname="cs106l";
    std::string location="online";
    std::string language="c++";
    return{classname,location,language};

}

int main(){

    auto [classname,location,language]=getclassinfo();
    std::cout<<"join us"<<location<<;
    return 0;
}

• 语法：auto [var1,var2,···，varn]=expression;
• the expression =a data structure whose size is always known at compile time
• vector 的大小不确定（动态分配）故不可以用，the std::vector data structure does not have a known size at compile time

example usage with c++ data structure

vector

map

• 获得map元素 std::mapages{ {"alice",25}, {"bob",30}, {"charlie",35} };

ages["alice"]; ages.at("bob");

• 优点：
• ubiquitous,works for all objects in c++
• enforces type-safey disallowing narrowing-conversions
• 缺点：
• 与uniform initialization重载冲突

引用

rich memory semantics core: the idea of reference

definition: an alias to something that already exists in memory using &