向量<对<双精度，双精度>>给出问题

vector<pair<double,double>> giving problems

本文关键字：双精度 lt gt 出问题 向量      更新时间：2023-10-16
#include <iostream>
#include <string>
#include <vector>
using namespace std;
typedef vector<pair<double, double> > Vec; //cords vector (0.0,0.0)/(x,y)
typedef pair<double, double> Punto; //single coord
int main()
{
    int x;
    cout << "cuants vertex?" << endl;
    cin >> x;
    Vec V[x]; // Declare vector of pairs as long as user wants
    Punto P;
    for (int i = 0; i < V.size(); i++) { //fill vector with coords
        cout << "Introdueix coordenada numero: " << i;
        cout << "x: ";
        cin >> P.first;
        cout << "y: ";
        cin >> P.second;
        V.push_back(P);
    }
    for (int c = 0; c < V.size(); c++) { //show all coords
        P.first = V[c].first;
        P.second = V[c].second;
        cout << P.first << P.second << endl;
    }
}

这是一个填充vector<pair<double,double>>的简单代码，它给出了这个错误：

main.cpp: In function ‘int main()’:
main.cpp:16:18: error: request for member ‘size’ in ‘V’, which is of non-class type ‘Vec [x] {aka std::vector > [x]}’
   for(int i=0;i<V.size(); i++){
                   ^~~~
main.cpp:19:5: error: request for member ‘push_back’ in ‘V’, which is of non-class type ‘Vec [x] {aka std::vector > [x]}’
    V.push_back(P);
      ^~~~~~~~~
main.cpp:21:19: error: request for member ‘size’ in ‘V’, which is of non-class type ‘Vec [x] {aka std::vector > [x]}’  
for(int c=0; c<V.size(); c++){
                 ^~~~
main.cpp:22:16: error: ‘Vec {aka class std::vector >}’ has no member named ‘first’
    P.first=V[c].first;
                 ^~~~~
main.cpp:23:17: error: ‘Vec {aka class std::vector >}’ has no member named ‘second’; did you mean ‘end’?   
P.second=V[c].second;
              ^~~~~~

有什么方法可以解决吗？

这一行：

Vec V[x]; // Declare vector of pairs as long as user wants

实际上是在创建一个C风格的Vec数组，而不是单个Vec。您应该改用圆括号，构造单个Vec：

Vec V(x); // Declare vector of pairs as long as user wants

但是，现在push_back将添加其他元素。取代

V.push_back(P);

跟

V[i] = P;

Vec V[x];

x 不是常量表达式，因此您声明的是可变长度数组。 这是一个编译器扩展，不是C++。 数组不能有.size()成员。

您需要将其更改为：

Vec V;

(此外，使用 Vec::size_type 遍历向量，否则您将收到签名警告。

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