Fork and printf buffering issues

printf Output conditions:

(1) Call fflush;

(2) the buffer is full;

(3) encountered \ r \ n These characters

(4) Encounter scanf these to take the buffer;

(5) The thread or process exits;

The buffer of the parent process is copied after the fork;

Code:

1#include <unistd.h>2#include <stdio.h>3 4 5 intGlob =6;6 CharBuf[] ="a write to stdout\n";7 8 intMain ()9 {Ten     int var; One pid_t pid; A  -     var= the; -  the     if(Write (Stdout_fileno, buf,sizeof(BUF)-1) !=sizeof(BUF)-1){ -Perror ("Write error\n"); -         return-1; -     } +  -printf"before fork\n"); +  A     if(PID = fork ()) <0){ atPerror ("Fork error\n"); -         return-1; -}Else if(PID = =0){ -glob++; -         var++; -}Else { inSleep (2); -     } to  +printf"pid =%d, Glob =%d, var =%d\n", Getpid (), Glob,var); -  the     return 0; *}

Results:

[Email protected] forkprintf]#GCCFORKPRINTF.C-o forkprintf[[email protected] forkprintf]#./FORKPRINTFAWriteTo Stdoutbefore forkpid=17098, Glob =7, var = thePID=17097, Glob =6, var = the[email protected] forkprintf]#./forkprintf >Tmp.out[[email protected] forkprintf]#CatTmp.outaWriteTo Stdoutbefore forkpid=17106, Glob =7, var = thebefore Forkpid=17105, Glob =6, var = the

(1) For the first time input to the console, write unbuffered direct output, printf ("before fork\n") there is a \ n line buffer identity direct output, and the child process copies the parent process code snippet, and then output the last printf;

(2) The second input to the file, write unbuffered direct output, printf ("before fork\n") into a fully buffered and no output, the child process copies the parent process buffer and code snippet, so when the parent-child process exits, flush buffer, there are two printf output;

Fork and printf buffering issues