push_back和emplace_back区别1. 测试代码2. 分析

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我是靠谱客的博主拼搏发带，这篇文章主要介绍push_back和emplace_back区别1. 测试代码2. 分析，现在分享给大家，希望可以做个参考。

1. 测试代码

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#include <iostream>
#include <vector>
using namespace std;

class A {
 public:
  A(int i, int j) : i_(i), j_(j){
    cout << "normal construct function" << endl;
  }
  A(const A& a) {
    cout << "copy construct function" << endl;
  }
  A(const A&& a) {
    cout << "move construct function" << endl;
  }
 private:
  int i_, j_;
};
int main() {
  vector<A> v;
  v.reserve(20);

  cout << "create a object: " << endl;
  A a(1,2);
  cout << endl;

  cout << "v.push_back(a): " << endl;
  v.push_back(a);
  cout << endl;

  cout << "v.push_back(move(a)): " << endl;
  v.push_back(move(a));
  cout << endl;

  cout << "v.emplace_back(2,3): " << endl;
  v.emplace_back(2,3);
  cout << endl;

  cout << "v.emplace_back(a): " << endl;
  v.emplace_back(a);
  cout << endl;

  cout << "v.emplace_back(move(a)): " << endl;
  v.emplace_back(move(a));
  cout << endl;

  return 0;
}

普通构造函数参数设置为2个，避免隐式构造

结果如下：

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create a object:
normal construct function

v.push_back(a):
copy construct function

v.push_back(move(a)):
move construct function

v.emplace_back(2,3):
normal construct function

v.emplace_back(a):
copy construct function

v.emplace_back(move(a)):
move construct function