4th. Pipeline and FIFO

4.1 Piping

Pipelines are created by the pipe function and provide a one-way data stream.

Header file	#include <unistd.h>
Function prototypes	int pipe (int fd[2]);
return value	The success is 0, the error is-1
function function	The function returns two file descriptors: Fd[0] and fd[1]. FD[0] used for read operations, Fd[1] to write operations
Description	Pipelines can only be used for affinity interprocess communication. To achieve non-affinity interprocess communication with a well-known pipeline FIFO

4.2 Pipe for half-duplex communication

Steps to implement:

(1) Creating pipelines (Fd[0] and fd[1])

(2) Fork

(3) The parent process closes the read end of the pipe (fd[0])

(4) Sub-process close the write end of the pipeline (Fd[1])

(5) Parent process writes data to the write end of the pipeline (Fd[1])

(6) The sub-process reads the data from the read end of the pipe (fd[0])

1#include <stdio.h>2#include <stdlib.h>3#include <unistd.h>4 5 #defineRead_max_len 106 7 intMain ()8 {9pid_t Childpid =0;Ten     intpipefd[2] = {0}; One     CharBuf[read_max_len +1] = {0}; A  -     if(Pipe (PIPEFD) <0) -     { theprintf"Pipe Error");  -         return-1; -     } -  +Childpid =fork (); -  +     if(Childpid <0) A     { atprintf"Fork error\n"); -         return-1; -     } -  -     //Child Process -     if(Childpid = =0) in     { -Close (pipefd[1]);  to  +Read (pipefd[0], buf, Read_max_len); -printf"child:%s\n", buf); the  *Exit0); $     }Panax Notoginseng      -     //Parent Process theClose (pipefd[0]); +  AWrite (pipefd[1],"Hello",sizeof("Hello")); theprintf"parent:%s\n","Hello"); +  -Waitpid (Childpid, NULL,0); $  $     return 0; -}

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4.3 Pipeline for full duplex communication

Steps to implement:

(1) Create Pipelines 1 (fd1[0] and fd1[1]), Pipe 2 (fd2[0] and fd2[1])

(2) Fork

(3) Parent process closes the read end of Pipe 1 (fd1[0]), closes the write end of Pipe 2 (fd2[1])

(4) Sub-process closes the write end of pipe 1 (fd1[1]), closes the read end of Pipe 2 (fd2[0])

(5) Communication between parent and child processes

4.4 Popen and Pclose functions

Header file	#include <stdio.h>
Function prototypes	FILE *popen (const char *command, const char *type);
	int Pclose (FILE *stream);
return value	Successfully returned file descriptor, failed to return null
Parameters	Command	Shell command, this line of command will be uploaded to Bin/sh and use the-C flag
	Type	R: Read the standard output of the Commond
		W: standard input written to command
Description	The file descriptor created by Popen must be closed by Pclose.

1#include <stdio.h>2#include <string.h>3 4 #defineBuf_max_len 1005 6 intMain ()7 {8FILE *FP =NULL;9     CharBuf[buf_max_len +1] = {0};Ten  Onefp = Popen ("ls","R"); A     if(fp = =NULL) -     { -printf"Popen error\n");  the         return-1; -     } -  -      while(Fgets (buf, Buf_max_len, fp)! =NULL) +     { - fputs (buf, stdout); +     } A  at Pclose (FP); -  -     return 0; -}

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4.5 FIFO

4th. Pipeline and FIFO