關於linux select無須多說， 來看程式碼：

1. #include<stdio.h>
2. #include<string.h>
3. #include<stdlib.h>
4. #include<unistd.h>
5. #include<sys/time.h>
6. #include<sys/types.h>
8. int main(int argc, char *argv[])
9. {
10. if
    (argc != 2)
11. {
12. printf( "para error\n");
13. return -1;
14. }
16. struct
    timeval tv; // 超時時間
17. tv.tv_sec = 10;
18. tv.tv_usec = 500; // 注意單位是微秒
20. fd_set rdfds;
21. FD_ZERO(&rdfds); // 描述集初始化
23. unsigned int n = atoi(argv[ 1]);
24. printf( "n is %u\n", n);
25. for( unsigned int i = 0; i < n; i++)
26. {
27. FD_SET(i, &rdfds);
28. }
30. printf( "to select\n");
31. select(n, &rdfds, NULL, NULL, &tv);
33. return 0;
34. }

1. xxxxxx:~/network&gt; g++ -g server.cpp
2. server.cpp: 34: 2: warning: no newline at end of file
3. xxxxxx:~/network&gt; ./a.out 2000
4. n is 2000
5. Segmentation fault (core dumped)
6. xxxxxx:~/network&gt; gdb a.out core
7. GNU gdb 6.6
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13. This GDB was configured as "i586-suse-linux"...
14. Using host libthread_db library "/lib/libthread_db.so.1".
16. warning: Can 't read pathname for load map: Input/output error.
17. Reading symbols from / lib/libonion.so...done.
18. Loaded symbols for / lib/libonion.so
19. Reading symbols from /usr/ lib/libstdc++.so .6...done.
20. Loaded symbols for /usr/ lib/libstdc++.so .6
21. Reading symbols from / lib/libm.so .6...done.
22. Loaded symbols for / lib/libm.so .6
23. Reading symbols from / lib/libgcc_s.so .1...done.
24. Loaded symbols for / lib/libgcc_s.so .1
25. Reading symbols from / lib/libc.so .6...done.
26. Loaded symbols for / lib/libc.so .6
27. Reading symbols from / lib/libdl.so .2...done.
28. Loaded symbols for / lib/libdl.so .2
29. Reading symbols from / lib/ld-linux.so .2...done.
30. Loaded symbols for / lib/ld-linux.so .2
31. Core was generated by `
32. Program terminated with signal 11, Segmentation fault.
33. #0 0x080485af in main (argc=-1, argv=0xffffffff) at server.cpp:27
34. 27 FD_SET(i, &amp;rdfds);
35. (gdb)

1. static __inline__ void __FD_SET( unsigned long fd, __kernel_fd_set *fdsetp)
2. {
3. unsigned long _tmp = fd / __NFDBITS;
4. unsigned long _rem = fd % __NFDBITS;
5. fdsetp->fds_bits[_tmp] |= ( 1UL<<_rem);
6. }
8. #define __NFDBITS (8 * sizeof(unsigned long))
10. typedef struct {
11. unsigned long fds_bits [__FDSET_LONGS];
12. } __kernel_fd_set;
14. #define __FDSET_LONGS (__FD_SETSIZE/__NFDBITS)
16. #define __FD_SETSIZE 1024