c++ - 保留然后分配给 std::string

Question

如果我调整大小然后分配一个 std::string 如下

std::string str;
str.resize(4);
str[1] = 'A'; // No problem

应该没有问题，但是如果我reserve然后assign

std::string str;
str.reserve(4);
str[1] = 'A'; // ?

会不会有问题？我读到元素未初始化并且大小没有增加。那么用 [] 运算符赋值给一个元素有意义吗？

Answer 1

来自 cplusplus

By reserving a capacity for the string of at least the size of the entire file, we try to avoid all the automatic reallocations that the object str could suffer each time that inserting a new character would make its length surpass its capacity.

reserve 不会增加字符串的大小，只是说明下次重新分配时需要增加多少。