value.h

PostgreSQL 8.2中增加了很多企业用户所需要的功能和性能上的提高,其开发团队说,该版本将加速更多企业向该数据库移植.核心开发成员之一Bruce Momjian表示,在新版PostgreSQL

/*-------------------------------------------------------------------------
 *
 * value.h
 *	  interface for Value nodes
 *
 *
 * Copyright (c) 2003-2006, PostgreSQL Global Development Group
 *
 * $PostgreSQL: pgsql/src/include/nodes/value.h,v 1.5 2006/03/05 15:58:57 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#ifndef VALUE_H
#define VALUE_H

#include "nodes/nodes.h"

/*----------------------
 *		Value node
 *
 * The same Value struct is used for five node types: T_Integer,
 * T_Float, T_String, T_BitString, T_Null.
 *
 * Integral values are actually represented by a machine integer,
 * but both floats and strings are represented as strings.
 * Using T_Float as the node type simply indicates that
 * the contents of the string look like a valid numeric literal.
 *
 * (Before Postgres 7.0, we used a double to represent T_Float,
 * but that creates loss-of-precision problems when the value is
 * ultimately destined to be converted to NUMERIC.	Since Value nodes
 * are only used in the parsing process, not for runtime data, it's
 * better to use the more general representation.)
 *
 * Note that an integer-looking string will get lexed as T_Float if
 * the value is too large to fit in a 'long'.
 *
 * Nulls, of course, don't need the value part at all.
 *----------------------
 */
typedef struct Value
{
	NodeTag		type;			/* tag appropriately (eg. T_String) */
	union ValUnion
	{
		long		ival;		/* machine integer */
		char	   *str;		/* string */
	}			val;
} Value;

#define intVal(v)		(((Value *)(v))->val.ival)
#define floatVal(v)		atof(((Value *)(v))->val.str)
#define strVal(v)		(((Value *)(v))->val.str)

extern Value *makeInteger(long i);
extern Value *makeFloat(char *numericStr);
extern Value *makeString(char *str);
extern Value *makeBitString(char *str);

#endif   /* VALUE_H */