select()的細節

直接先看code

 1: #include <sys/types.h>
 2: #include <sys/select.h>
 3: #include <stdio.h>
 4: #include <stdlib.h>
 5: #include <string.h>
 6: 
 7: #define BUFSIZE (256)
 8: 
 9: int main(void){
10:     fd_set read_fdset;
11:     int maxfd=1;
12:     char buff[BUFSIZE];
13:     while (1) {
14:         FD_ZERO(&read_fdset);
15:         FD_SET(0, &read_fdset);
16:         int result = select(maxfd + 1, &read_fdset, NULL, NULL, NULL);
17:         if (0 > result){
18:             printf("select error\n");
19:             exit(1);
20:         }   
21: 
22:         if (FD_ISSET(0, &read_fdset)){
23:             printf("data is ready\n");
24:             int c=getc(stdin);
25:             printf("%c",c);
26:         }   
27:     }   
28:     return 0;
29: }

結果是?輸入test，按下兩次enter，得到的結果，如下圖

如果可以一眼看出答案，表示對select()有深入了解。容我賣個關子，這裡問題出在於stdio對於buffer以及kernel buffer的認知上面