可以使用 vector 的 empty() 或 size() 成员函数判断,如下:
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> vec;
cout << "empty: " << boolalpha << vec.empty() << endl;
cout << "size: " << vec.size() << endl;
vec.push_back(123);
vec.push_back(456);
cout << "empty: " << boolalpha << vec.empty() << endl;
cout << "size: " << vec.size() << endl;
system("pause");
return 0;
}