用于评论目的的大括号范围是否会降低C代码的速度？

除了以下代码片段的代码本身之外,您应该专注于代码结构.

#include <iostream>
#include <utility>
#include <vector>
#include <string>

int main()
{
    std::string str = "Hello";
    std::vector<std::string> v;

    {// uses the push_back(const T&) overload,which means 
     // we'll incur the cost of copying str
        v.push_back(str);
        std::cout << "After copy,str is "" << str << ""n";

        //other code involves local variable
     }

    {// uses the rvalue reference push_back(T&&) overload,// which means no strings will be copied; instead,the contents
     // of str will be moved into the vector.  This is less
     // expensive,but also means str might now be empty.
        v.push_back(std::move(str));
        std::cout << "After move,str is "" << str << ""n";

        //other code involves local variable
   }

    std::cout << "The contents of the vector are "" << v[0]
                                     << "","" << v[1] << ""n";
}