c++ - `std::vector` 会做任何我没有要求的事情吗

Question

在 C++ 中，如果我初始化一个 std::vector v(100); 并且从不尝试 resize() 或 reserve() 它，capacity() 是否保证始终保持不变？我想确保没有内存 alloc/freeing/realloc/etc 出于性能原因而进行。 (是的，这会影响性能；我的函数一直被调用，它们必须快速返回)。

恢复一切:

std::vector<float> v;
// somehow, `v' is initialized to have 100 elements
void f() { // this function must return _very_ quickly
    /* do some processing, without ever calling v.resize() or v.reserve(), but
       accesing v.size() and v[i] all the time */
    /* it is guaranteed that no system calls (such as memory management)
       will take place here? */
} // no objects on the stack whose destroyers might try to `delete' anything.

Answer 1

来自 C++11 23.3.6.3“vector 容量”中关于 vector::reserve() 的评论:

It is guaranteed that no reallocation takes place during insertions that happen after a call to reserve() until the time when an insertion would make the size of the vector greater than the value of capacity().