CvSeq 序列

最新推荐文章于 2017-10-09 15:38:26 发布

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最新推荐文章于 2017-10-09 15:38:26 发布

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分类专栏： OpenCV函数

本文链接：https://blog.youkuaiyun.com/z397164725/article/details/8362371

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本文深入探讨了CvSeq内存存储器中对象的特性及其内存存储方式，包括序列创建、元素访问、序列清理和序列块提取等关键操作。详细解释了序列属性、内存管理与优化策略，旨在帮助开发者更高效地利用CvSeq进行数据组织与处理。

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CvSeq 内存存储器中可以存储的一种对象。定义如下：

#define CV_TREE_NODE_FIELDS(node_type)                          \
    int       flags;         /* micsellaneous flags */          \
    int       header_size;   /* size of sequence header */      \
    struct    node_type* h_prev; /* previous sequence */        \
    struct    node_type* h_next; /* next sequence */            \
    struct    node_type* v_prev; /* 2nd previous sequence */    \
    struct    node_type* v_next /* 2nd next sequence */

/*
   Read/Write sequence.
   Elements can be dynamically inserted to or deleted from the sequence.
*/
#define CV_SEQUENCE_FIELDS()                                            \
    CV_TREE_NODE_FIELDS(CvSeq);                                         \
    int       total;          /* total number of elements */            \
    int       elem_size;      /* size of sequence element in bytes */   \
    char*     block_max;      /* maximal bound of the last block */     \
    char*     ptr;            /* current write pointer */               \
    int       delta_elems;    /* how many elements allocated when the seq grows */ \
    CvMemStorage* storage;    /* where the seq is stored */             \
    CvSeqBlock* free_blocks; /* free blocks list */                    \
    CvSeqBlock* first; /* pointer to the first sequence block */

typedef struct CvSeq
{
CV_SEQUENCE_FIELDS()
}
CvSeq;

/* Creates new empty sequence that will reside in the specified storage */
CVAPI(CvSeq*) cvCreateSeq( int seq_flags, int header_size,
int elem_size, CvMemStorage* storage );

创建序列：header_size 序列的头大小一般为sizeof(CvSeq) 除使用CV_SEQUENCE_FIELDS()扩展时，按扩展后大小

elem_size 序列存储元素大小

storage 为序列指定内存存储器

seq_flags 由3个类值组成 1元素类型2序列性质（集合、曲线、二叉树、图）3序列其它属性（闭合、简单、凸、嵌套）

/* Removes all the elements from the sequence. The freed memory
can be reused later only by the same sequence unless cvClearMemStorage
or cvRestoreMemStoragePos is called */
CVAPI(void) cvClearSeq( CvSeq* seq );清空序列中所有元素。内存返还内存存储器，不返还系统。

/* Retrives pointer to specified sequence element.
Negative indices are supported and mean counting from the end
(e.g -1 means the last sequence element) */
CVAPI(char*) cvGetSeqElem( const CvSeq* seq, int index );访问指定元素

/* Calculates index of the specified sequence element.
Returns -1 if element does not belong to the sequence */
CVAPI(int) cvSeqElemIdx( const CvSeq* seq, const void* element,
CvSeqBlock** block CV_DEFAULT(NULL) );

检测元素是否在序列中，若block不空，返回该元素地址：该函数并非查询序列中内容相同的元素，而是查找元素的位置是否在序列中。

CV_INLINE CvSeq* cvCloneSeq( const CvSeq* seq, CvMemStorage* storage CV_DEFAULT(NULL))
{
return cvSeqSlice( seq, CV_WHOLE_SEQ, storage, 1 );
}

复制一个序列，对cvSeqSlice的简单封装。

/* Extracts sequence slice (with or without copying sequence elements) */
CVAPI(CvSeq*) cvSeqSlice( const CvSeq* seq, CvSlice slice,
CvMemStorage* storage CV_DEFAULT(NULL),
int copy_data CV_DEFAULT(0));