Openrtmfp/Cumulus primer (13) local memory chip for Io Management

Openrtmfp/Cumulus primer (13) local memory chip for Io Management

• Author: Liu Da-poechant (Zhong Chao)
• Email: zhongchao. USTC # gmail.com (#-> @)
• Blog: blog.csdn.net/poechant
• Date: 10000l 24^{Th, 2012}

First, this class is not used in openrtmfp/Cumulus, so you can close the current tab of your browser to avoid wasting time.

In the memorystreambuf introduced in "openrtmfp/Cumulus primer (10) stream buffer for Io Management", there is a friend named scopedmemoryclip, which is what this article will introduce

First, the most important thing is that scopedmemoryclip has a memorystreambuf member.

class ScopedMemoryClip {public:    ScopedMemoryClip(MemoryStreamBuf& buffer,Poco::UInt32 offset);    ~ScopedMemoryClip();private:    void                clip(Poco::Int32 offset);    Poco::UInt32        _offset;    MemoryStreamBuf&   _buffer;};

1 Constructor

The parameters passed in by the constructor correspond to the two member values of scopedmemoryclip. The offset cannot exceed the online value of the memorystremambuf buffer.

ScopedMemoryClip::ScopedMemoryClip(MemoryStreamBuf& buffer, UInt32 offset)    : _offset(offset), _buffer(buffer) {    if (_offset >= _buffer._bufferSize)        _offset = _buffer._bufferSize - 1;    if (_offset < 0)        _offset = 0;    clip(_offset);}

2 destructor

ScopedMemoryClip::~ScopedMemoryClip() {    clip(-(Int32)_offset);}

3 buffer Cutting

We can see that both the constructor and the Destructor call the clip function. This function completes the buffer and forms a local memory chip:

• If the input offset parameter is positive, only the last part after the cut is retained.
• If the input parameter is negative, it is equivalent to expanding the buffer area forward. (Only occurs in destructor)

The source code is as follows.

Void scopedmemoryclip: Clip (int32 offset) {// obtain gptr char * gpos = _ buffer. gcurrent (); // offset the buffer address and modify the buffer size _ buffer. _ pbuffer + = offset; _ buffer. _ buffersize-= offset; // The Position of the pptr minus the new address of the buffer, which is used as the new position of the pptr int PPOs = _ buffer. pcurrent ()-_ buffer. _ pbuffer; // set the gptr reachable zone and location _ buffer. setg (_ buffer. _ pbuffer, gpos, _ buffer. _ pbuffer + _ buffer. _ buffersize); // set the reachable regions and locations of pptr _ buffer. setp (_ buffer. _ pbuffer, _ buffer. _ pbuffer + _ buffer. _ buffersize); _ buffer. pbump (PPOs); // if the number of written data is smaller than the offset, you can set the number of written data to zero if (_ buffer. _ written <OFFSET) _ buffer. _ written = 0; // if the number of written data is greater than or equal to the offset, offset else _ buffer is subtracted. _ written-= offset; // if the number of written nodes is greater than the buffer capacity, it is set to the buffer capacity if (_ buffer. _ written> _ buffer. _ buffersize) _ buffer. _ written = _ buffer. _ buffersize ;}

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Reprinted, please indicate the csdn blog from LIU Da: blog.csdn.net/poechant

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