向量Initializer_list

Question

我正在尝试使用我自己的类实现一个向量，所以我不能完成初始化器列表部分

# include <iostream>
# include <exception>
# include<initializer_list>
template <class T>
 class vector {
  public:
  T* a;
T n;
int pos, c;
vector() { a = 0; n = 0; }
vector(T n) : n(n) { a = new T[n]; }
vector(std::initializer_list <vector> l) {
    a = new T[int(sizeof(l))];
        for (int f : l)
            *(a + f) = l.begin() + f;
     }
 void push_back(T k) {
    int i = k;
    *(a + n) = k;
}
 vector& operator= (vector&& th) {
     this->a = th.a;
    th.a = nullptr; return (*this);
}
vector& operator=(vector& k)
{
    this->a = k.a;
    return(*this);
}
int  size() { return n; }
void pop_back() { *(a + n) = nullptr;
n--;
}
void resize(int c) {  
    delete a;
    n = c;
 a = new T[c];
 }
 T operator[](int pos) {
    if (pos > sizeof(a))
        std::cout << "out of range";

    else return *(a + pos);
 }
 };
 int main() {
vector<int> a(10);
vector<char>b{ 'w','b','f','g' };
getchar();
return 0;

}

我只是尝试使用指针偏移量表示法将初始化器列表项放入动态数组中，但我收到错误VS 17 IDE

Severity    Code    Description Project File    Line    Suppression   
Error   C2440   '=': cannot convert from 'const _Elem *' to 'T' 
Error   C2440   'initializing': cannot convert from 'const _Elem' to 'int'

Answer 1

你好，尼姆罗德！

#include <iostream>
#include <exception>
#include <initializer_list>
// normally people don't place a space between '#' and 'include'

template <class T>
class vector {
public:
    T* a;
    int n;
    // probably it is length the vector
    // change T to int
    int pos, c;
    vector() { 
        a = nullptr;
        // do not use '0' to instruct null pointer 
        n = 0; 
    }

    vector(int n): n(n) { a = new T[n]; }

    vector(std::initializer_list<T> l) {
        a = new T[l.size()];
        // redundant force cast from size_t to int

        for (int i = 0; i < l.size(); i++) {
            a[i] = l.begin()[i];
        }
        // for (int f : l) # it seems that you wrote JavaScript before?
        //     *(a + f) = l.begin() + f;
    }

    void push_back(T k) {
        // assigns "T k" to "int i"? it's confusing

        // int i = k;
        // *(a + n) = k;
    }

    // probably still many problems
    vector& operator=(vector&& th) {
        this->a = th.a;
        th.a = nullptr;
        return (*this);
    }

    vector& operator=(vector& k) {
        this->a = k.a;
        return(*this);
    }

    int size() { return n; }

    void pop_back() { *(a + n) = nullptr;
        n--;
    }

    void resize(int c) {  
        delete a;
        n = c;
        a = new T[c];
    }

    T operator[](int pos) {
        if (pos > sizeof(a))
            std::cout << "out of range";
        else return *(a + pos);
    }
 };

int main() {
    vector<int> a(10);
    vector<char>b{ 'w','b','f','g' };
    getchar();
    return 0;
}

你仍然需要更多的练习。XP

在你的代码上下文中，int.

• Range for loop的模板变量应该是T而不是initializer_list<T>，initializer_list<T>会在

1. 中取值。因此，它应该属于T.