系统编程之文件IO（五）——实战训练

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
int read_line(int fd, char *buffer, int max_len)
{
    int i;
    int ret;
    char temp;
    for (i = 0; i < max_len; i++)
    {
        ret = read(fd,&temp,1);
        if (ret < 0)
        {
            perror("read error!");
            exit(1);
        }
        if(ret == 0)
        {
            break;            
        }
        if (temp == '\n')
        {
            break;
        }
        buffer[i] = temp;
    }
    buffer[i] = '\0';
    return i;
}
int main(int argc, char *argv[])
{
    int fd;
    if ((fd = open(argv[1], O_RDWR | O_CREAT, 0655)) == -1)
    {
        perror("open file error!");
        _exit(1);
    }
    char buffer[1024];
    for (size_t i = 0; i < 3; i++)
    {
        memset(buffer, 0, sizeof(buffer));
        printf("Please input data:\n");
        scanf("%s",buffer);
        if(write(fd,buffer,strlen(buffer)) < 0)
        {
            perror("write data error!");
            exit(1);
        }
        write(fd,"\n",1);
    }
    memset(buffer, 0, sizeof(buffer));
    lseek(fd, 0, SEEK_SET);
    while((read_line(fd,buffer,sizeof(buffer) - 1)) != 0)
    {
        printf("buffer = %s\n",buffer);
        memset(buffer, 0, sizeof(buffer));
    }
    close(fd);
    return 0; 
}