问题描述
不知道该如何叙述这个问题，请看代码：
#include <set>#include <iostream>using namespace std;struct test { int data[3];};int main(void) { test t1; set<test> s; s.insert(t1); s.begin()->data[0] = 1;//此处赋值报错：read-only variable is not assignable return 0;}
应该是set内部的问题吧？求高人解释，非常感谢...
问题解答
回答1：set内的元素不可以更改，只能增加或者删除。http://www.cplusplus.com/refe...
Sets are containers that store unique elements following a specific order.In a set, the value of an element also identifies it (the value is itself the key, of type T), and each value must be unique. The value of the elements in a set cannot be modified once in the container (the elements are always const), but they can be inserted or removed from the container.Internally, the elements in a set are always sorted following a specific strict weak ordering criterion indicated by its internal comparison object (of type Compare).set containers are generally slower than unordered_set containers to access inpidual elements by their key, but they allow the direct iteration on subsets based on their order.Sets are typically implemented as binary search trees.回答2：
意思好像是：只读的变量是不能被赋值的。。。
回答3：set的迭代器是只读的，不允许修改（因为set内部有将元素排序，随意更改元素的值可能会破坏其有序性）；
要改变元素的值，只能先把旧的删除，再把新的插入进去
