在c语言中，写入另一个程序的标准输出/从另一个程序的标准输出读取

Question

这是一个家庭作业问题。我有3个程序A, B和C，它们不是父/子进程，而是单独的程序。B必须将消息("Hello")写入a的标准输入，并从c的标准输出中读取另一条消息("Hello")。我应该使用哪个概念来实现它?我四处找了一段时间，但没有找到合适的东西。我想我应该使用先进先出，但我不能重定向管道。我可以使用先进先出dup2吗?如果是，怎么做?这不是作业本身的问题，这只是作业的方式。然后我会在上面实现其他东西。(我可以张贴我的fifo基础代码，如果是这样的话，只是不要这样做，因为我不确定)

Answer 1

如果我理解错了问题请告诉我。

假设您创建了程序A, B和C。在编程上，您可以使用man 1 mkfifo或man 3 mkfifo来创建命名管道。

然后你的每一个进程将open(2)他们和使用dup2(2)根据他们的需要。

例如，程序A可以这样重定向它的stdout:

int fifo = open("fifo_1", O_WRONLY);
dup2(fifo, 1);

或程序B可以像这样重定向stdin和stdout:

int fifo_in = open("fifo_1", O_RDONLY);
int fifo_out = open("fifo_2", O_WRONLY);
dup2(fifo_in, 0);
dup2(fifo_out, 1);

Answer 2

我按照@chrk的解释修改了这段代码。这是《高级Unix编程》一书中的FIFO示例。一个简单的服务器-客户机示例。客户端发送三个小写字符串到服务器，服务器将它们变成大写并通过FIFO发送回客户端("FIFO #clientpid"是客户端FIFO的名称)。客户端将它们打印到标准输出。所以我修改了它，在接收到来自客户端的消息后，服务器将大写字符串写入客户端的STDINT。客户机从标准输出中读取它们并打印到标准输出中。正如我所预料的那样。谢谢你的帮助。首先，我以错误的方式实现。在chrk代码的帮助下，我又写了一遍。下面是代码:

客户的输出

client 2941 started
client 2941: applesauce --> APPLESAUCE
client 2941: tiger --> TIGER
client 2941: mountain --> MOUNTAIN
Client 2941 done

服务器:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <ctype.h>
#define ec_neg1(s,m) if((s) == -1) {perror(m); exit(errno);}
#define SERVER_FIFO_NAME "fifo_server"
#define PERM_FILE        0664
struct simple_message {
pid_t sm_clientpid;
char sm_data[200];
};

int main()
{
  int fd_server, fd_client, i;
  ssize_t nread;
  struct simple_message msg;
  char fifo_name[100];
  printf("server startedn");
  if (mkfifo(SERVER_FIFO_NAME, PERM_FILE) == -1 && errno != EEXIST)
  {perror("can't make fifo"); exit(errno); }
  ec_neg1( fd_server = open(SERVER_FIFO_NAME, O_RDWR), "cant open fd_server" )
  while (1) 
  {
     ec_neg1( nread = read(fd_server, &msg, sizeof(msg)), "can't read from fd_server")
     if (nread == 0) {
       errno = ENETDOWN;
       perror("nread == 0"); exit(errno);
      }
     for (i = 0; msg.sm_data[i] != ''; i++)
       msg.sm_data[i] = toupper(msg.sm_data[i]);
     make_fifo_name(msg.sm_clientpid, fifo_name, sizeof(fifo_name));
     ec_neg1( fd_client = open(fifo_name, O_WRONLY), "can't open fifo_name" )
     ec_neg1( write(fd_client, &msg, sizeof(msg)), "can't write to fd_client" )
     ec_neg1( close(fd_client), "can't close fd_client" )
   }
/* never actually get here */
 ec_neg1( close(fd_server), "can't close fd_server" )
 exit(EXIT_SUCCESS);
 return 0;
 }

int make_fifo_name(pid_t pid, char *name, size_t name_max)
{
 snprintf(name, name_max, "fifo%ld", (long)pid);
 return 0;
}

客户

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#define ec_neg1(s,m) if((s) == -1) {perror(m); exit(errno);}
#define SERVER_FIFO_NAME "fifo_server"
#define PERM_FILE        0664
struct simple_message {
pid_t sm_clientpid;
char sm_data[200];
};

int make_fifo_name(pid_t pid, char *name, size_t name_max)
{
 snprintf(name, name_max, "fifo%ld", (long)pid);
 return 0;
}
int main()
{
 int fd_server, fd_client = -1, i;
 ssize_t nread;
 struct simple_message msg;
 char fifo_name[100];
 char *work[] = {
   "applesauce",
   "tiger",
   "mountain",
   NULL
 };
 printf("client %ld startedn", (long)getpid());
 msg.sm_clientpid = getpid();
 make_fifo_name(msg.sm_clientpid, fifo_name,
       sizeof(fifo_name));
 if (mkfifo(fifo_name, PERM_FILE) == -1 && errno != EEXIST)
   {perror("can't make fifo"); exit(errno); }
 ec_neg1( fd_server = open(SERVER_FIFO_NAME, O_WRONLY), "can't open fd_server" )
 for (i = 0; work[i] != NULL; i++) 
 {
   strcpy(msg.sm_data, work[i]);
   ec_neg1( write(fd_server, &msg, sizeof(msg)),"can't write to fd_server" )
   if (fd_client == -1){
     ec_neg1( fd_client = open(fifo_name, O_RDWR), "can't open fifo_name"  )
     ec_neg1(dup2(fd_client, 0), "can't duplicate stdin")
   }
     ec_neg1( nread = read(0, &msg, sizeof(msg)), "can't read from fd_client" )
   if (nread == 0) {
       errno = ENETDOWN;
       perror("nread == 0"); exit(errno);
   }
   printf("client %ld: %s --> %sn", (long)getpid(),
             work[i], msg.sm_data);
 }
 ec_neg1( close(fd_server), "can't close fd_server" )
 ec_neg1( close(fd_client), "can't close fd_client" )
 ec_neg1( unlink(fifo_name), "can't unlink fifo_name" )
 printf("Client %ld donen", (long)getpid());
 exit(EXIT_SUCCESS);
}