如果我没有定义向量大小，程序将崩溃 [英] Program crashes if I don't define a vector size

问题描述

当前正在学习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，但是如果我定义大小 std :: vector< ; int> example（1）可以正常工作。我还注意到，如果我使用 example.push_back（27）而不是 example [0] = 27 而不定义大小也可以。

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

空向量没有在内存中分配任何元素。

An empty vector has no elements allocated in memory.

您应该使用 example.push_back（27）而不是尝试对其进行下标。 push_back（）分配一个新元素，然后将其添加到向量中。一旦将该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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