c++ - 指向 vector 的指针

Question

下面的代码有什么问题

vector < double >* a;
a->push_back(25);
a->push_back(30);
a->push_back(15);
a->push_back(40);
cout << a->at(2) << endl;

它应该打印 15，但它什么也没打印

Answer 1

a 是一个指针，但未正确初始化...它必须像:

int main()
{
    std::vector<double>* a = new std::vector<double>;
    a->push_back(25);
    a->push_back(30);
    a->push_back(15);
    a->push_back(40);
    std::cout << a->at(2) << std::endl;
    delete a;
    return 0;
}