尝试使用管道读取/写入另一个程序

Question

我正在尝试编写一个程序，它读取另一个程序的输出并写入程序作为输入。

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 int main(void)
 {
     char str[30];

     printf("Input string : ");
     fflush(stdout);
     scanf("%s", &str);
     fflush(stdout);

     printf("entered string is %s\n", str);
     return 0;
 }

此程序1是从stdin读取输入的简单程序，并打印输入的字符串。在program2中，我尝试创建2个管道并执行program1。并读取program1的输出并获取用户输入并将输入的字符串用户传递给program1。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>

typedef struct pipe_rw
{
   pid_t cpid;
   int pipe_r[2];
   int pipe_w[2];
} RWPIPE;

char *get_user_input(void)
{
   char buf[128];
   char *input;
   char ch;
   int n;
   int len = 0;

   memset(buf, 0x0, 128);
   while((ch = fgetc(stdin)) != 0xa)
   {
      buf[len] = ch;
      len++;
   }

   input = malloc(sizeof(char) * (len));
   strncpy(input, buf, (len));
   return input;
}

int pclose_rw(RWPIPE *rwp)
{
   int status, ret = 0;

   if (rwp)
   {
      if (rwp->cpid > 0)
      {
         kill(rwp->cpid, SIGTERM);

         do {
            ret = waitpid(rwp->cpid, &status, WUNTRACED|WCONTINUED);
         } while (!WIFEXITED(status) && !WIFSIGNALED(status));
      }

      close(rwp->pipe_r[0]);
      close(rwp->pipe_w[1]);
      free(rwp);
   }

   return ret;
}

RWPIPE *popen_rw(const char *command)
{
   RWPIPE *rwp = (RWPIPE *)malloc(sizeof(*rwp));
   if (rwp == NULL)
      return NULL;

   memset(rwp, 0x00, sizeof(*rwp));
   if (pipe(rwp->pipe_r) != 0 || pipe(rwp->pipe_w) != 0)
   {
      free(rwp);
      return NULL;
   }

   rwp->cpid = fork();
   if (rwp->cpid == -1)
   {
      free(rwp);
      return NULL;
   }

   if (rwp->cpid == 0)
   {
      dup2(rwp->pipe_w[0], STDIN_FILENO);
      dup2(rwp->pipe_r[1], STDOUT_FILENO);

      close(rwp->pipe_r[0]);
      close(rwp->pipe_r[1]);
      close(rwp->pipe_w[0]);
      close(rwp->pipe_w[1]);

      execl(command, command, NULL);
      printf("Error: fail to exec command - %s ..\n", command);
      exit (1);
   }
   else
   {
      close(rwp->pipe_r[1]);
      close(rwp->pipe_w[0]);
   }

   return rwp;
}

ssize_t read_p(RWPIPE *rwp, void *buf, size_t count)
{
   return read(rwp->pipe_r[0], buf, count);
}

ssize_t write_p(RWPIPE *rwp, const void *buf, size_t count)
{
   return write(rwp->pipe_w[1], buf, count);
}

int main(void)
{
   char rbuf[BUFSIZ], wbuf[BUFSIZ];
   int ret, len, n = 0;
   char *string;

   RWPIPE *rwp = popen_rw("./read_write");
   if (rwp == NULL)
   {
      printf("Error: fail to open command ..\n");
      return EXIT_FAILURE;
   }

   while (1)
   {
      memset(rbuf, 0x00, sizeof(rbuf));
      if (read_p(rwp, rbuf, sizeof(rbuf)) < 1)
      {
         printf("No more input..\n");
         break;
      }
      printf("%s", rbuf);

      string = get_user_input();
      len = strlen(string);
      ret = write_p(rwp, string, len);
      if (ret != len)
      {
         printf("Write %d bytes (expected %d) ..\n", ret, len);
         break;
      }
      printf("end");
   }
   pclose_rw(rwp);

   return EXIT_SUCCESS;
}

如果运行，程序2成功读取program1的输出。并且它获得用户输入但是它无法将从用户输入的字符串提供给program1。

[root@localhost test_code]# ./rw_pipe
Input string : 1234



^C

请给我一些想法，为什么它这样工作。