Pipe design for unknown pipelines in Linux

1 function description pipe (pipeline creation): 1) header file include & lt; unistdh & gt; 2) definition function: intpipe (int

1. function description

Pipe (pipeline creation ):
1) header file # include
2) define the function: int pipe (int filedes [2]);
3) function description: pipe () creates an MPs queue and returns the file description words from the filedes array.
Filedes [0] is the read end in the pipeline
Filedes [1] is the write end of the MPs queue.
4) return value: if it succeeds, zero is returned. otherwise,-1 is returned. the error cause is stored in errno.

Error code:
The EMFILE process has used up the maximum number of file descriptions
The ENFILE system does not have a file description word available.
The filedes array address of the EFAULT parameter is invalid.

Example:

Root @ wl-MS-7673:/home/wl/desktop/c ++ # cat-n pipe_test.cpp 1 2 # include
 
  
3 # include
  
   
4 # include
   
    
5 # include
    
     
6 # include
     
      
7 # include
      
        8 # include
       
         9/* 10 * program entry 11 **/12int main () 13 {14int pipe_fd [2]; 15pid_t pid; 16 char buf_r [100]; 17char * p_wbuf; 18int r_num; 19 20 memset (buf_r, 0, sizeof (buf_r); 21 22/* create pipeline */23if (pipe (pipe_fd) <0) 24 {25 printf ("pipe create error \ n"); 26 return-1; 27} 28 29/* create sub-process */30if (pid = fork ()) = 0) // sub-process execution sequence 31 {32 printf ("\ n"); 33 close (pipe_fd [1]); // the sub-process first closes the write end 34 sleep (2) of the pipeline;/* let the parent process run first, in this way, the parent process writes the child process to read the content */35if (r_num = rea D (pipe_fd [0], buf_r, 100)> 0) 36 {37 printf ("% d numbers read from the pipe is % s \ n", r_num, buf_r ); 38} 39 close (pipe_fd [0]); 40 exit (0); 41} 42 else if (pid> 0) // execution sequence of the parent process 43 {44 close (pipe_fd [0]); // the parent process first closes the read end 45if (write (pipe_fd [1], "Hello", 5 )! =-1) 46 printf ("parent write1 Hello! \ N "); 47if (write (pipe_fd [1]," Pipe ", 5 )! =-1) 48 printf ("parent write2 Pipe! \ N "); 49 close (pipe_fd [1]); 50 wait (NULL);/* wait until the sub-process ends */51 exit (0); 52} 53 return 0; 54} 55 56root @ wl-MS-7673:/home/wl/desktop/c ++ # g ++ pipe_test.cpp-o pipe_testroot @ wl-MS-7673:/home/wl/desktop/c ++ #. /pipe_test parent write1 Hello! Parent write2 Pipe! 10 numbers read from the pipe is Hello Piperoot @ wl-MS-7673:/home/wl/desktop/c ++ #
       
      
     
    
   
  
 

Before creating a fork, create an MPs queue by using pipe (), and then create a child process by using fork. then, the child process copies the code segment/data segment and stack segment of the parent process, therefore, the created pipeline will be copied, the child process, and the parent process. to make the pipeline communicate normally, the existing pipeline must be processed.