Parent-child inter-process communication model implementation (POPEN)

0, FILE *popen (const char *command, const char *type);

The Popen function is equivalent to doing several things:

1. Create a nameless pipe file

2. Fork ()

3, in the sub-process, EXEC command

4, in the sub-process,

if type = = "R", it is equivalent to:

int fd_new =  fopen ("pipe_name", O_rdonly);d up2 (0, fd_new );

if type = = "W", it is equivalent to:

int fd_new =  fopen ("pipe_name", O_wronly);d up2 (0 , fd_new);

5. The return value is a file pointer to the pipe file type operation

1, read the way Popen

In P1:

1 " R ") ;

Popen return value fp_in file pointer is a read-file pointer to the pipe file

In P2:

Popen (, "R") redirects the standard output in the P2 to the pipe file, which is equivalent to the pipe file fputs

1 printf ("%s\n", SRC);

Specific code:

P1:

1#include <stdio.h>2#include <string.h>3#include <stdlib.h>4 intMainintargcChar* argv[])//./my_reverse5 {    6printf"PID:%d\n", Getpid ());7file*fp_in;8     Charcmd[1024x768] ;9     Charstr[1024x768] ;Ten      while(Memset (str,0,1024x768), Fgets (str,1024x768, stdin)! =NULL) One     { Amemset (CMD,0,1024x768); -sprintf (CMD,"%s%s", argv[1], str); -fp_in = Popen (cmd,"R") ; the         if(fp_in = =NULL) -         { -Perror ("Popen"); -Exit1); +         } -memset (str,0,1024x768) ; +FSCANF (fp_in,"%s", str); Aprintf"Res:%s\n", str); at  -     } -     return 0 ; -}

P2:

1#include <stdio.h>2#include <string.h>3#include <stdlib.h>4 voidHandleChar*str)5 {6     intBG, end;7     inttmp;8BG =0; 9end = strlen (str)-1;Ten      while(BG <end) One     { ATMP =STR[BG]; -STR[BG] =Str[end]; -Str[end] =tmp; theBG + + ; -End-- ; -     } - } + intMainintargcChar* argv[])//Argv[1] - {     +     Charsrc[1024x768] ; Astrcpy (SRC, argv[1]); at handle (SRC); -printf"%s\n", SRC); -     return 0 ; -}

2, to write the way Popen

In P1:

1 fp_out = Popen (argv[1"w");

The return value of Popen is the write-file pointer to the pipe file

In P2:

Popen (, "W") redirects the standard input in the P2 to the pipe file, which is equivalent to from the pipe file fgets

1

Specific code:

P1:

1#include <stdio.h>2#include <string.h>3#include <stdlib.h>4 intMainintargcChar* argv[])//./my_reverse5 {    6printf"PID:%d\n", Getpid ());7file*fp_out;8     Charcmd[1024x768] ;9     Charstr[1024x768] ;TenFp_out = Popen (argv[1],"W") ; One     if(Fp_out = =NULL) A     { -Perror ("Popen"); -Exit1); the     } -      while(Memset (str,0,1024x768), Fgets (str,1024x768, stdin)! =NULL) -     { - fputs (str, fp_out); + fflush (fp_out); -  +     } A Pclose (fp_out); at     return 0 ; -}

P2:

1#include <stdio.h>2#include <string.h>3#include <stdlib.h>4 voidHandleChar*str)5 {6     intBG, end;7     inttmp;8BG =0; 9end = strlen (str)-1;Ten      while(BG <end) One     { ATMP =STR[BG]; -STR[BG] =Str[end]; -Str[end] =tmp; theBG + + ; -End-- ; -     } - } + intMainintargcChar*argv[]) - {     +     Charsrc[1024x768] ; A      while(Memset (SRC,0,1024x768), gets (SRC)! =NULL) at     { - handle (SRC); -printf"pid:%d%s\n", Getpid (), SRC); -     } -     return 0 ; -}

Parent-child inter-process communication model implementation (POPEN)