C++ 新的带有初始化器的 if 语句

Question

“if”语句的 cppreference 页面；

https://en.cppreference.com/w/cpp/language/if

给出了下面的例子；

Except that names declared by the init-statement (if init-statement is a declaration) and names declared by condition (if condition is a declaration) are in the same scope, which is also the scope of both statements Blockquote

std::map<int, std::string> m;
if (auto it = m.find(10); it != m.end()) { return it->size(); }

这是一个错字，不是吗？我没有遗漏任何东西，我应该遗漏任何东西；

it->second.size(); 

或

it->first;

没有？

Answer 1

是的，这是一个错字。 iterator对于 std::map将被取消引用为 std::map::value_type , 其中value_type是std::pair<const Key, T> .

参见 std::map::find 的用法示例(来自 cppreference):

#include <iostream>
#include <map>
int main()
{  
    std::map<int,char> example = {{1,'a'},{2,'b'}};

    auto search = example.find(2);
    if (search != example.end()) {
        std::cout << "Found " << search->first << " " << search->second << '\n';
    } else {
        std::cout << "Not found\n";
    }
}