c++ - 使用vector没有头文件为啥不报错？

Question

include <opencv2/opencv.hpp>

include <iostream>

include <cassert>

include <cmath>

include <fstream>

using namespace std;
using namespace cv;

C++程序，使用了opencv，上面是头文件和命名空间，程序里有vector，为啥不报错，能正常编译运行？

Answer 1

因为OpenCV有cv::vector…

Answer 2

并没有存在。。

Answer 3

opencv里是应该有类似这样的代码

include <vector>

namespace cv {
using std::vector;
}

Answer 4

你用的是cv::vector，而不是std::vector