Automatically Allocated Buffer Class. More...

#include "utility.hpp"

Collaboration diagram for cv::AutoBuffer< _Tp, fixed_size >:

Public Types
typedef _Tp	value_type

Public Member Functions
	AutoBuffer ()
	the default constructor More...

	AutoBuffer (size_t _size)
	constructor taking the real buffer size More...

	AutoBuffer (const AutoBuffer< _Tp, fixed_size > &buf)
	the copy constructor More...

	~AutoBuffer ()
	destructor. calls deallocate() More...

void	allocate (size_t _size)
	allocates the new buffer of size _size. if the _size is small enough, stack-allocated buffer is used More...

void	deallocate ()
	deallocates the buffer if it was dynamically allocated More...

	operator _Tp * ()
	returns pointer to the real buffer, stack-allocated or heap-allocated More...

	operator const _Tp * () const
	returns read-only pointer to the real buffer, stack-allocated or heap-allocated More...

AutoBuffer< _Tp, fixed_size > &	operator= (const AutoBuffer< _Tp, fixed_size > &buf)
	the assignment operator More...

void	resize (size_t _size)
	resizes the buffer and preserves the content More...

size_t	size () const
	returns the current buffer size More...

Protected Attributes
_Tp	buf [(fixed_size > 0)?fixed_size:1]
	pre-allocated buffer. At least 1 element to confirm C++ standard requirements More...

_Tp *	ptr
	pointer to the real buffer, can point to buf if the buffer is small enough More...

size_t	sz
	size of the real buffer More...

Detailed Description

template<typename _Tp, size_t fixed_size = 1024/sizeof(_Tp)+8>
class cv::AutoBuffer< _Tp, fixed_size >

Automatically Allocated Buffer Class.

The class is used for temporary buffers in functions and methods. If a temporary buffer is usually small (a few K's of memory), but its size depends on the parameters, it makes sense to create a small fixed-size array on stack and use it if it's large enough. If the required buffer size is larger than the fixed size, another buffer of sufficient size is allocated dynamically and released after the processing. Therefore, in typical cases, when the buffer size is small, there is no overhead associated with malloc()/free(). At the same time, there is no limit on the size of processed data.

This is what AutoBuffer does. The template takes 2 parameters - type of the buffer elements and the number of stack-allocated elements. Here is how the class is used:

void my_func(const cv::Mat& m)
{
   cv::AutoBuffer<float> buf(1000); // create automatic buffer containing 1000 floats
   buf.allocate(m.rows); // if m.rows <= 1000, the pre-allocated buffer is used,
                         // otherwise the buffer of "m.rows" floats will be allocated
                         // dynamically and deallocated in cv::AutoBuffer destructor
   ...
}