为什么我在这个C++代码中得到了一个未定义的引用

我正在努力学习如何使用gperf库进行完美的哈希在Ubuntu 14.04计算机上。我遇到编译器错误。有人能帮我解决这个问题？

gperf是一个库，当提供一组静态密钥进行散列时例如，英语词典中的单词会产生C或C++包含完美哈希函数和哈希表本身的代码。

这是代码。产生的函数是in_word_set，它是用户函数I将用于查询哈希表，in_word_set使用hash函数将关键字映射到哈希表中。

我用于生成哈希表的键是SOWPODS拼字词典的前10个单词，您可以在下面的单词列表数组中看到。

当我用g++编译时，我得到的错误是这样的。

[~/Desktop]$ g++ -g -Wall  fun.cpp -lm                   
/tmp/ccUb0GiA.o: In function `main':
/home/gaurish108/Desktop/fun.cpp:149: undefined reference to `in_word_set(char const*, unsigned int)'
collect2: error: ld returned 1 exit status

这是我正在使用的代码。main函数在最后。

/* C code produced by gperf version 3.0.4 */
/* Command-line: gperf sowpods_bkp.txt  */
/* Computed positions: -k'3,5' */
#include <string.h>
#include <iostream>

#if !((' ' == 32) && ('!' == 33) && ('"' == 34) && ('#' == 35) 
      && ('%' == 37) && ('&' == 38) && (''' == 39) && ('(' == 40) 
      && (')' == 41) && ('*' == 42) && ('+' == 43) && (',' == 44) 
      && ('-' == 45) && ('.' == 46) && ('/' == 47) && ('0' == 48) 
      && ('1' == 49) && ('2' == 50) && ('3' == 51) && ('4' == 52) 
      && ('5' == 53) && ('6' == 54) && ('7' == 55) && ('8' == 56) 
      && ('9' == 57) && (':' == 58) && (';' == 59) && ('<' == 60) 
      && ('=' == 61) && ('>' == 62) && ('?' == 63) && ('A' == 65) 
      && ('B' == 66) && ('C' == 67) && ('D' == 68) && ('E' == 69) 
      && ('F' == 70) && ('G' == 71) && ('H' == 72) && ('I' == 73) 
      && ('J' == 74) && ('K' == 75) && ('L' == 76) && ('M' == 77) 
      && ('N' == 78) && ('O' == 79) && ('P' == 80) && ('Q' == 81) 
      && ('R' == 82) && ('S' == 83) && ('T' == 84) && ('U' == 85) 
      && ('V' == 86) && ('W' == 87) && ('X' == 88) && ('Y' == 89) 
      && ('Z' == 90) && ('[' == 91) && ('' == 92) && (']' == 93) 
      && ('^' == 94) && ('_' == 95) && ('a' == 97) && ('b' == 98) 
      && ('c' == 99) && ('d' == 100) && ('e' == 101) && ('f' == 102) 
      && ('g' == 103) && ('h' == 104) && ('i' == 105) && ('j' == 106) 
      && ('k' == 107) && ('l' == 108) && ('m' == 109) && ('n' == 110) 
      && ('o' == 111) && ('p' == 112) && ('q' == 113) && ('r' == 114) 
      && ('s' == 115) && ('t' == 116) && ('u' == 117) && ('v' == 118) 
      && ('w' == 119) && ('x' == 120) && ('y' == 121) && ('z' == 122) 
      && ('{' == 123) && ('|' == 124) && ('}' == 125) && ('~' == 126))
/* The character set is not based on ISO-646.  */
error "gperf generated tables don't work with this execution character set. Please report a bug to <bug-gnu-gperf@gnu.org>."
#endif

#define TOTAL_KEYWORDS 16
#define MIN_WORD_LENGTH 2
#define MAX_WORD_LENGTH 10
#define MIN_HASH_VALUE 2
#define MAX_HASH_VALUE 21
/* maximum key range = 20, duplicates = 0 */
#ifdef __GNUC__
__inline
#else
#ifdef __cplusplus
inline
#endif
#endif
static unsigned int hash (register const char *str, register unsigned int  len)
{
  static unsigned char asso_values[] =
    {
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 10, 22,
      22,  0,  0,  0, 22, 22, 15, 22,  5, 22,
      22, 22,  0, 22, 22, 22,  5,  0, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
      22, 22, 22, 22, 22, 22
    };
  register int hval = len;
  switch (hval)
    {
      default:
        hval += asso_values[(unsigned char)str[4]];
      /*FALLTHROUGH*/
      case 4:
      case 3:
        hval += asso_values[(unsigned char)str[2]];
      /*FALLTHROUGH*/
      case 2:
        break;
    }
  return hval;
}
#ifdef __GNUC__
__inline
#if defined __GNUC_STDC_INLINE__ || defined __GNUC_GNU_INLINE__
__attribute__ ((__gnu_inline__))
#endif
#endif
const char *in_word_set (register const char *str, register unsigned int len)
{
  static const char * wordlist[] =
    {
      "", "",
      "AA",
      "AAH",
      "AAHS",
      "AARGH",
      "AARRGH",
      "AARRGHH",
      "AARDWOLF",
      "",
      "AARDWOLVES",
      "AAHING",
      "",
      "AARDVARK",
      "AARDVARKS",
      "AAHED",
      "", "",
      "AAL",
      "AALS",
      "AALII",
      "AALIIS"
    };
  if (len <= MAX_WORD_LENGTH && len >= MIN_WORD_LENGTH)
    {
      register int key = hash (str, len);
      if (key <= MAX_HASH_VALUE && key >= 0)
        {
          register const char *s = wordlist[key];
          if (*str == *s && !strcmp (str + 1, s + 1))
            return s;
        }
    }
  return 0;
}

int main()
{
  in_word_set("AA",2);
 return 0;
}