Re: Segmentation Fault !

[Hans Aberg]

At 17:51 +0530 2001/03/24, Rutu Raghu Manchiganti [T] wrote:
>I am making a parser using lex and yacc..not flex and bison..so sorry
>for posting the  message on this group.
...
>I get a segmentation fault when i try 2 allocate some memory..here is
>the sample code..
>[a-zA-Z-]+[0-9]* { yylval.name = (char*)malloc(strlen(yytext) + 1);
>                   strcpy(yylval.name, yytext);
>                   return IDENTIFIER; }
>
>This works fine for the first time and gives a segmentation fault the
>second time !!

Flex \0 terminates yytext, so it appears correct under Flex, except that
you have a memory leak, and could better write malloc(yyleng + 1).

So check what Yacc does, or switch to Flex and Bison
  ftp://ftp.digital.com/pub/GNU/non-gnu/flex/flex-2.5.4a.tar.gz
  ftp://alpha.gnu.org/gnu/cvs/

I compile under C++, and use
  class my_type {
  public:
    std::string text;
    ...
  };
  #define YYSTYPE my_type
and in Flex:
  yylval.text = std::string(yytext, yyleng);

This way I avoid memory leaks, and I do not have to worry about correct
allocation. (For more details, see the archives of the help-bison and
bug-bison list.)

  Hans Aberg