C++ cout 不显示任何内容 [英] C++ cout not displaying anything

问题描述

什么可以解释为什么 cout 在这段代码中没有显示任何内容?我知道它与行 v[0] = 1; 有关.但我不知道为什么，有人对此有解释吗?

What may explain why the cout is not displaying anything in this code? I know it's related to the line v[0] = 1; but I can't find out why, does someone have an explanation for it?

我也知道改变 v[0] = 1;对于 v.push_back(1);就能解决问题.

I also know that changing v[0] = 1; for v.push_back(1); would solve the problem.

#include <iostream> 
#include <vector> 

using namespace std; 

int main() 
{ 
    vector<int> v; 
    v[0] = 1; 
    cout << "Hello" << endl; 
    return 0; 
}

推荐答案

你不能做 v[0]=1 因为你还没说向量 v 有多少个元素代码> 有.所以它会导致运行时错误(它崩溃)

You cannot do v[0]=1 because you haven't said how many elements the vector v has. So it causes run time error(it crashes)

将其声明为 vectorv(10)(这表示 v 将有 10 个元素)并使用 v[0]=1

Declare it as vector<int>v(10) (this says that v will have 10 elements) and use v[0]=1

或

如果您事先不知道矢量大小，请使用 v.push_back(1);

If you don't know the vector size beforehand use v.push_back(1);

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