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c++11新加入了emplace_back():
如果要将一个临时变量push到容器的末尾，push_back()需要先构造临时对象，再将这个对象拷贝到容器的末尾，而emplace_back()则直接在容器的末尾构造对象，这样就省去了拷贝的过程。
请看代码：
#include <iostream> #include <cstring> #include <vector> using namespace std;
class A { public: A(int i){ str = to_string(i); cout << "构造函数" << endl; }
~A(){} A(const A& other): str(other.str){ cout << "拷贝构造" << endl; } public:
string str; }; int main() { vector<A> vec; vec.reserve(10); for(int
i=0;i<10;i++){ vec.push_back(A(i)); //调用了10次构造函数和10次拷贝构造函数, //
vec.emplace_back(i); //调用了10次构造函数一次拷贝构造函数都没有调用过 } }
