Why am I getting an undefined reference in this C++ code?

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I am trying to learn how to use the gperf library for perfect hashing on an Ubuntu 14.04 computer. I am getting compiler errors. Can someone help me out with this?

gperf is a library which when provided with a set of static keys to hash like for example words in an english dictionary will produce C or C++ code containing the perfect hash function and the hash-table itself.

Here is the code. The functions produced are in_word_set which is the function I, the user, will use to query the hash table and hash function used by in_word_setto map the key-word into the hash-table.

The keys I used for generating the hash-table were the first 10 words of the SOWPODS scrabble dictionary which you can see in the word-list array below.

The error I get when I compile with g++ is this.

[~/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

Here is the code I am using. main function is at the very end.

/* 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 <[email protected]>."
#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;
}
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This is a bug in gperf 3.0.4, caused by complicated semantics of __gnu_inline__ in C++ mode. You have two possible workarounds:

  • Use optimization (g++ -O instead of g++).
  • Regenerate your .cpp file using gperf 3.1.