C/C++学习笔记
关于STL
- vector
- 1关于vector初始的capacity不够的如何处理
//windows下的增长，如果不够,多分配原先的50%，至少+1.
void push_back(value_type&& _Val)
{
...
_Reserve(1);
...
}
void _Reserve(size_type _Count)
{ // ensure room for _Count new elements, grow exponentially
if (_Unused_capacity() < _Count)
{ // need more room, try to get it
if (max_size() - size() < _Count)
_Xlen();
_Reallocate(_Grow_to(size() + _Count));
}
}
size_type _Grow_to(size_type _Count) const
{ // grow by 50% or at least to _Count
size_type _Capacity = capacity();
_Capacity = max_size() - _Capacity / 2 < _Capacity
? 0 : _Capacity + _Capacity / 2; // try to grow by 50%
if (_Capacity < _Count)
_Capacity = _Count;
return (_Capacity);
}
//linux下增加一倍 代码不贴了 懒
- 2vector什么时候释放分配的内存 destory释放数据,只调用<>内部数据的析构，并移除该位置，不释放vec分配的空间. 只有调用析构函数才会释放对应的存储空间，故对于越来越大的vector采用swap一个空vector能更好的减少内存占用
template<class _Ty> inline
_Ty *_Allocate(size_t _Count, _Ty *)
{ // allocate storage for _Count elements of type _Ty
void *_Ptr = 0;
if (_Count == 0)
;
else if (((size_t)(-1) / sizeof (_Ty) < _Count)
|| (_Ptr = ::operator new(_Count * sizeof (_Ty))) == 0)
_Xbad_alloc(); // report no memory
return ((_Ty *)_Ptr);
}
void deallocate(pointer _Ptr, size_type)
{ // deallocate object at _Ptr, ignore size
::operator delete(_Ptr);
}