recorddel.c

linux下

#include<stdlib.h>
#include<stdio.h>
#include<sys/types.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<string.h>
#include<unistd.h>                          /*sys_ftruncate*/
#include"table.h"



int record_delete(const char* szTableName,T_Conditions* pConditions)   /*ɾ�zTableName���pConditionsƥ�ļ�,�ļ��*/
{
	return do_record_delete(table_open(szTableName),pConditions);
}


int do_record_delete(T_TableDes*  pTableDes,T_Conditions* pConditions)
{
	int nPos=0;     
	void* pRecord;
	//int nRetPos;
	long fd=pTableDes->fd;
	int ndelcount=0;              /*�ļ��*/


	struct stat  statbuf;


	pRecord=malloc(pTableDes->pTableHeader->nRecSize);            /*��һ��Ŀռ��ڴ�����һ��*/

	while((nPos<pTableDes->pTableHeader->nValidRecordCount)&&(record_search(pTableDes,pConditions,&nPos)>=0))
	{                                                              /*�Ҳ�,ز�ҵļ��*/
		if(nPos<pTableDes->pTableHeader->nValidRecordCount)        /*�ü���һ����һ�����λ�;*/
		{
			lseek(fd,-(pTableDes->pTableHeader->nRecSize),SEEK_END);   /*�ļ��һ��*/
			read(fd,pRecord,(pTableDes->pTableHeader->nRecSize));

			lseek(fd,(pTableDes->pTableHeader->nDataOffset+
			nPos*(pTableDes->pTableHeader->nRecSize)),SEEK_SET);/*�һ��ǵ˼�,ɾ�˼�*/                                              		  /*�һ��дü�Ŷ���,Ǹü�*/
			write(fd,pRecord,(pTableDes->pTableHeader->nRecSize));
		}
		if(fstat(fd,&statbuf)<0)
		{
		free(pRecord);
		free(pTableDes->pTableHeader);
		free(pTableDes->pColInfos);
		free(pTableDes->pRecFields);
		free(pTableDes);

		close(fd);

		perror("fstat");
		exit(EXIT_FAILURE);
		}
		    /*�ļС�������fdijȵ�ϵͳ�sys_fstat*/
		ftruncate(fd,(statbuf.st_size-pTableDes->pTableHeader->nRecSize));    /*�ԭȥһ���sys_ftruncate*/

		pTableDes->pTableHeader->nValidRecordCount--;	/*��1*/

		do_table_show(pTableDes);

		ndelcount++;                                     /*ɾļ���*/
		//nPos=nRetPos;                                   /*Ӹü�ż����*/
	}

		lseek(fd,sizeof(NULL),SEEK_SET);                   //更新表头信息,记录个数变了
		write(fd,pTableDes->pTableHeader,sizeof(T_TableHeader));

	if(fsync(fd)==-1)			/*�дش��*/
	{
		free(pRecord);
		free(pTableDes->pTableHeader);
		free(pTableDes->pColInfos);
		free(pTableDes->pRecFields);
		free(pTableDes);

		close(fd);

		perror("file synchronize failed");
		exit(EXIT_FAILURE);
	}							/*ر�ļ*/

	return ndelcount;
}