Question

我在我的程序中遇到一个问题，我需要从客户端到服务器带一个字符串，然后服务器将使用该字符串创建一个私有FIFO。但是，当我在客户端上提示时键入一个名称，然后尝试在服务器上继续时，它会出错：没有文件或目录存在。

另外，我不明白如何将整数从服务器移动到客户端，因为write（）方法不起作用（似乎只适用于字符和字符串）。

客户机侧：

main (void)
{
  int fda;  // to write to server
  int fdb;  // to read response from server
  int mem_req[1];   // buffer holds a #
  char outchar[7];  // server puts string here
  char pfifo_name[10];

  memset(mem_req,0,1); 
  memset(outchar,0,7); 
  memset(pfifo_name,0,10);

  printf("\nClient: Please enter a private FIFO name (less than 10 chars): ");
  scanf("%s", &pfifo_name);

  printf("\nClient: Please enter a memory request number: ");
  scanf("%d", &mem_req);

  if((fda=open("FIFO1", O_WRONLY))<0)
     printf("cant open fifo to write");

  if((fdb=open(pfifo_name, O_RDONLY))<0)
     printf("cant open fifo to read");




  write(fda, mem_req, 1);
  write(fda, pfifo_name, 10);
  printf("\nClient: Pfifo and memory request sent to server ");
  read(fdb, outchar, 7);
  printf("\nClient: received from server %s", outchar);

  close(fda);
  close(fdb);

  printf ("\nall done!\n");

了Serverside：

     main (void)
{
  int fda;  // to read from client
  int fdb;  // to write to client
  int finish;   // lets me know that client is done
  int i;    // because C needs this defined as int
  int fr_size; // frame size for memory management
  int temp_mem;
  int n_frame = 0;
  int o_frame = 0;
  int n_byte = 0;
  int o_byte = 0;
  int fr_num = 0;
  int byte_num;

  char mem_req[1];  // buffer holds a character
  char outchar[7];  // server puts string here
  char pfifo_name[10]; //client provides server a private fifo name

  memset(mem_req,0,1); 
  memset(outchar,0,7); 
  memset(pfifo_name,0,10);

  printf("\nServer: Please enter a desired frame(page) size: ");
  scanf("%d", &fr_size);
  read(fda, pfifo_name, 10);
  /* Create the fifos and open them  */
  if ((mkfifo("FIFO1",0666)<0 && errno != EEXIST))
    {
    perror("cant create FIFO1");
    exit(-1);
    }

   if ((mkfifo(pfifo_name,0666)<0 && errno != EEXIST))
    {
    perror("cant create private fifo");
    exit(-1);
    }

  if((fda=open("FIFO1", O_RDONLY))<0)
     printf("cant open fifo to read");

  if((fdb=open(pfifo_name, O_WRONLY))<0)
     printf("cant open fifo to write");



  printf("\nServer: just got memeory request: ,%d", mem_req[0]);

  temp_mem = mem_req[0];

  n_frame = temp_mem/fr_size; // number of frames required for job
  n_byte = temp_mem - (n_frame * fr_size); // ending byte location

  write(fdb, &o_frame, sizeof(o_frame)); // output frame start location
  printf("\nServer: Frame start location sent");

  write(fdb, &o_byte, sizeof(o_byte));
  printf("\nServer: Byte start location sent");

  write(fdb, &n_frame, sizeof(n_frame));
  printf("\nServer: Frame end location sent");

  write (fdb, &n_byte, sizeof(n_byte));
  printf("\nServer: Byte end location sent");

  finish=read(fda, pfifo_name, 10);     //read the character

当编译器在服务器上获得mkfifo（pfifo_name，0666）＆lt; 0时，它会出错：

“无法创建私有fifo：不存在此类文件或目录”

我也从服务器上的所有4个写语句中收到错误（试图通过管道传递一个整数但它不起作用）

Answer 1

在服务器中：

read(fda, pfifo_name, 10);

这会失败，因为fda不包含有效的文件描述符，因为它从未初始化。

因此，没有任何内容被读入pfifo_name，因此它只保留0个字节（因为之前调用memset），即空字符串。然后将其传递给open，它会尝试打开一个空白名称的文件，该文件无效。

使用带有整数和字符串的FIFO（管道）发出问题

1 个答案: