系统 第二 天：如何插入数据的时候不覆盖

#include <stdio.h>
#include <errno.h>      //errno
#include <string.h>     //strerror()

/* lseek()  */
#include <sys/types.h>
#include <unistd.h>     //read()    write()

/* open()  */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

# define PER_IO_BYTES 4096
int main(int argc , char ** argv)
{
    

    char caFile[32] = {'\0'};
    strncpy(caFile,argv[1],sizeof(caFile));//复制

//  fd = open();
    int ret = -1;
    strcat(caFile,".old");//就是接上一个.old
    ret = rename(argv[1],caFile);
    if(-1==ret)
    {
        printf("rename error:%s\n",strerror(errno));
        return -1;
    }
    
    int fdNew = -1;
    fdNew = open(argv[1],O_WRONLY |O_CREAT,S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
    if(-1==fdNew)
    {
        printf("open error:%s\n",strerror(errno));
        return -1;
    }
    int fdOld=-1;
    fdOld = open(caFile,O_RDONLY);

    if(-1==fdOld)
    {
        printf("open error:%s\n",strerror(errno));
        return -1;
    }
    off_t offset = 0;
    printf("请输入位置：\n");
    scanf("%ld",&offset);
    char caBuf[PER_IO_BYTES] = {'\0'};
    int iLeft = offset;
    int iReaded = 0;
    while(iLeft)
    {
        if(iLeft >= PER_IO_BYTES)
        {
            ret = read(fdOld,caBuf,PER_IO_BYTES);
        }
        else
        {
            
            ret = read(fdOld,caBuf,iLeft);
        }
        if(-1==ret)
        {
            printf("read error:%s\n",strerror(errno));
            break;
        }

        iLeft -= ret;
        ret = write(fdNew,caBuf,ret);

        if(-1==ret)
        {
            printf("write error:%s\n",strerror(errno));
            break;
        }
    }
    char *pData = "$$$hljhkjhakfiewu$$$";
    ret = write(fdNew,pData,strlen(pData));
    if(-1 == ret)
    {
        printf("write error:%s\n",strerror(errno));
        return -1;
    }
    offset = lseek(fdOld,0,SEEK_CUR);
    while(1)
    {
        ret = read(fdOld,caBuf,PER_IO_BYTES);
        if(-1 == ret)
        {
            printf("read error :%s\n",strerror(errno));
        }
        else if(0 == ret)
        {
            break;
        }
        ret = write(fdNew,caBuf,ret);
        if(-1 == ret)
        {
            printf("write errorp:%s\n",strerror(errno));
            break;
        }
    }
    close (fdOld);
    close(fdNew);
    ret = remove(caFile);
    if(-1 == ret)
    {
            printf("remove  error:%s\n",strerror(errno));
            return -1;
    }

    return 0;
}