如果我没有定义矢量大小，程序会崩溃

Program crashes if I don#39;t define a vector size(如果我没有定义矢量大小，程序会崩溃)

问题描述

目前正在学习 C++，偶然发现了这个问题

Currently learning C++ and stumbled upon this problem

std::vector<int> example;

example[0] = 27;

std::cout << example[0];

这会使程序崩溃，但如果我定义一个大小 std::vector<int>示例(1) 它工作正常.我还注意到，如果我使用 example.push_back(27) 而不是 example[0] = 27 而不定义大小，它也可以正常工作.这背后有什么原因吗?

This crashes the program, but if I define a size std::vector<int> example(1) it works fine. What I also noticed was that if I use example.push_back(27) instead of example[0] = 27 without defining the size it also works fine. Is there a reasoning behind this?

推荐答案

一个空向量在内存中没有分配任何元素.

An empty vector has no elements allocated in memory.

您应该使用 example.push_back(27) 而不是尝试下标.push_back() 分配一个新元素，然后将其添加到向量中.一旦将新元素添加到向量中，就可以使用 example[0] = something 重新分配它.

You should use example.push_back(27) instead of trying to subscript it. push_back() allocates a new element and then adds it to the vector. Once that new element is added to the vector, it can be reassigned using example[0] = something.

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