创建一对父子进程： 父进程负责向文件中写入 长方形的长和宽 子进程负责读取文件中的长宽信息后，计算长方形的面积

 #include <myhead.h>
 int main(int argc, const char *argv[])
 {
     int retval=fork();
     if(retval>0){
         float length,width;
         int wfd=open("./rectangle",O_WRONLY|O_CREAT|O_TRUNC,0664);
         char buf[128]={0};
         printf("please enter length/width:");
         scanf("%f %f",&length,&width);
         while(getchar()!='\n');
     //  int size=strlen(buf);
         write(wfd,&length,sizeof(float));
         write(wfd,&width,sizeof(float));
         close(wfd);
         sleep(4);
 
     }else if(retval==0){
         sleep(8);
         float length,width;
         int rfd=open("./rectangle",O_RDONLY);
         read(rfd,&length,sizeof(float));
         read(rfd,&width,sizeof(float));
         float area=length*width;
         printf("the area of rectangle is:%g \n",area);
         close(rfd);
                                                                                          
     }else if(retval==-1){
         perror("fork");
 
     }
     return 0;
 }