postgresql/src/backend/lib/stringinfo.c

/*-------------------------------------------------------------------------
 *
 * stringinfo.c--
 *	  These are routines that can be used to write informations to a string,
 *	  without having to worry about string lengths, space allocation etc.
 *	  Ideally the interface should look like the file i/o interface,
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/lib/stringinfo.c,v 1.8 1998/01/07 15:32:19 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <string.h>

#include <postgres.h>

#include <nodes/pg_list.h>
#include <lib/stringinfo.h>

/*---------------------------------------------------------------------
 * makeStringInfo
 *
 * Create a StringInfoData & return a pointer to it.
 *
 *---------------------------------------------------------------------
 */
StringInfo
makeStringInfo()
{
	StringInfo	res;
	long		size;

	res = (StringInfo) palloc(sizeof(StringInfoData));
	if (res == NULL)
	{
		elog(ABORT, "makeStringInfo: Out of memory!");
	}

	size = 100;
	res->data = palloc(size);
	if (res->data == NULL)
	{
		elog(ABORT,
		   "makeStringInfo: Out of memory! (%ld bytes requested)", size);
	}
	res->maxlen = size;
	res->len = 0;

	/*
	 * NOTE: we must initialize `res->data' to the empty string because we
	 * use 'strcat' in 'appendStringInfo', which of course it always
	 * expects a null terminated string.
	 */
	res->data[0] = '\0';

	return (res);
}

/*---------------------------------------------------------------------
 * appendStringInfo
 *
 * append to the current 'StringInfo' a new string.
 * If there is not enough space in the current 'data', then reallocate
 * some more...
 *
 * NOTE: if we reallocate space, we pfree the old one!
 *---------------------------------------------------------------------
 */
void
appendStringInfo(StringInfo str, char *buffer)
{
	int			buflen,
				newlen;
	char	   *s;

	Assert(str != NULL);
	if (buffer == NULL)
		buffer = "<>";

	/*
	 * do we have enough space to append the new string? (don't forget to
	 * count the null string terminating char!) If no, then reallocate
	 * some more.
	 */
	buflen = strlen(buffer);
	if (buflen + str->len >= str->maxlen - 1)
	{

		/*
		 * how much more space to allocate ? Let's say double the current
		 * space... However we must check if this is enough!
		 */
		newlen = 2 * str->len;
		while (buflen + str->len >= newlen - 1)
		{
			newlen = 2 * newlen;
		}

		/*
		 * allocate enough space.
		 */
		s = palloc(newlen);
		if (s == NULL)
		{
			elog(ABORT,
				 "appendStringInfo: Out of memory (%d bytes requested)",
				 newlen);
		}
		memmove(s, str->data, str->len + 1);
		pfree(str->data);
		str->maxlen = newlen;
		str->data = s;
	}

	/*
	 * OK, we have enough space now, append 'buffer' at the end of the
	 * string & update the string length. NOTE: this is a text string
	 * (i.e. printable characters) so 'strcat' will do the job (no need to
	 * use 'bcopy' et all...)
	 */
	strcat(str->data, buffer);
	str->len += buflen;
}