文件操作的一个小程序

题目：打开一个文件，若文件不存在，则创建文件并输入一传字符进文件。下次执行时，发现文件存在则输出文件内容
#include
#include
int main()
{
        int fd;
        char str[20]="",ch[20]="";
        if((fd=open("example",O_CREAT|O_EXCL|O_RDWR,S_IRUSR|S_IWUSR))>0)
        {
                printf("input message:");
                scanf("%s",str);
                str[strlen(str)]='\0';
                write(fd,str,strlen(str));
        }
        else
        {
                printf("file is exist!\n");
                fd=open("example",O_RDWR);
                read(fd,ch,20);
                printf("%s\n",ch);
        }
        close(fd);
        return 0;
}
对上边程序的改进（不用printf等，改用stdin,stdout）：
#include
#include
#include
#include
#include
int main()
{
        int fd,fp1,fp2;
        int ret;
        char str[20]="";

        if((fd=open("example",O_CREAT|O_EXCL|O_RDWR,S_IRUSR|S_IWUSR))>0)
        {
                printf("input message:");
                fp1=open("/dev/stdin",O_RDWR);
                ret = read(fp1,str,20);
//              str[ret-1]='\0';
                str[strlen(str)-1]='\0';
                write(fd,str,strlen(str));
                close(fp1);
        }
        else
        {
                printf("file is exist!\n");
                fd=open("example",O_RDWR);
                fp2=open("/dev/stdout",O_RDWR);
                read(fd,str,20);
                write(fp2,str,strlen(str));
                printf("\n");
        }
        close(fp2);
        close(fd);
        return 0;
}