select模型在win32API編程中也很常見,而且和linux中的select函數遵循同樣的berkeley標准,所以函數原型相同。select函數原型:
Ubuntu:
int select( int maxfdp, fd_set * readfds, fd_set * writefds, fd_set * errorfds, struct timeval * timeout);
Win32:
int select( intnfds, fd_set*readfds, fd_set*writefds, fd_set*exceptfds, const struct timeval*timeout);
可以看到是一樣的。不同點是,win32API中的select函數忽略第一個參數。而linux要求第一個參數設置成(參數2~4某個數組中文件描述符的最大值+1)。
下面是ubuntu10.0中使用select函數的一個例子,流程為:
Ubuntu10.0.4:
源代碼文件select.cpp:
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>// waitpid
#include <sys/types.h>// waitpid
#include <string.h>// strlen
/*
comment:
pipe is used between two processes on the same computer.
*/
#define TIMES 50
int main(){
int pipefds[2];
if( -1 == pipe( pipefds)){
printf( "Error when create pipes\n");
}else{
int i;
pid_t pid = fork();
if( 0 == pid){// child
printf( "child running\n");
close( pipefds[0]);
for( i = 0; i < TIMES; ++ i){
write( pipefds[1], "iamagoodguy", strlen( "iamagoodguy"));
sleep( 1);
}
}else{
printf( "parent running\n");
char buf[256];
close( pipefds[1]);
fd_set readfdset;// file descriptor set
for( i = 0; i < TIMES; ++ i){
FD_ZERO( & readfdset);
FD_SET( pipefds[0], & readfdset);// add read file descriptor
FD_SET( 0, & readfdset);// add standard input
select( pipefds[0]+1, & readfdset, NULL, NULL, NULL);
if( FD_ISSET( pipefds[0], & readfdset)){
buf[ read( pipefds[0], buf, 256)] = '\0';
printf( "Receive:%s\n", buf);
}
if( FD_ISSET( 0, & readfdset)){
buf[ read( 0, buf, 256)] = '\0';
printf( "Print:%s\n", buf);
}
}
int status;
wait( & status);
}
}
return 0;
}
還需要一個Makefile:
select: select.cpp
g++ $< -o $@
然後在命令行中鍵入:
make select
./select
運行截圖:
注意點
父進程必須等待子進程結束。如果父進程先於子進程結束,子進程成為死進程。
每次調用select後參數2都會被改變,下次調用select前必須重新設置。