Segmentation fault when initializing struct field by field

This is a discussion on Segmentation fault when initializing struct field by field within the C Programming forums, part of the General Programming Boards category; Hi All consider the following initialization of a struct: Code: #include <stddef.h> #include <stdlib.h> #include <regex.h> #include <stdio.h> #include <string.h> ...

  1. #1
    Registered User
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    May 2009
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    72

    Segmentation fault when initializing struct field by field

    Hi All

    consider the following initialization of a struct:

    Code:
    #include <stddef.h>
    #include <stdlib.h>
    #include <regex.h>
    #include <stdio.h>
    #include <string.h>
    
    struct CONFIG
     {
        int  *nos ;
        char *data_dir ;
        int *ratio ;
        regex_t *regex_int ;
        regex_t *regex_float ;
     } *_myconfig ;
    
    int main(void) {
      _myconfig = (struct CONFIG*)malloc(sizeof(_myconfig)) ;
      _myconfig->regex_int = calloc(1, sizeof(regex_t)) ;
      _myconfig->regex_float = calloc(1, sizeof(regex_t)) ;
      regcomp( _myconfig->regex_int, "[[:digit:]]+$", REG_EXTENDED | REG_NOSUB ) ;
      regcomp( _myconfig->regex_float, "^[[:digit:]]+\\.[[:digit:]]+$", REG_EXTENDED | REG_NOSUB ) ;
    
      printf("so far so good?") ;
      return 0;
    }
    If you run this code you'll get an Segmentation fault. However when I change the order of fields in the struct like

    Code:
    struct CONFIG
     {
        int  *nos ;
        char *data_dir ;
        regex_t *regex_int ;
        regex_t *regex_float ;
        int *ratio ;
     } *_myconfig ;
    Any suggestions whats happening here ?

    cheers
    LuCa

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
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    14,185
    Code:
     _myconfig = (struct CONFIG*)malloc(sizeof(_myconfig)) ;
    Well, that's not going to work. You need to have enough room for an entire struct, and 4 bytes certainly isn't. You should use sizeof(*_myconfig).

    (Edit: And there's no good reason to cast the result of malloc.)
    Last edited by tabstop; 06-07-2009 at 08:44 AM.

  3. #3
    Registered User
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    May 2009
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    72
    thats it, thanks!!!!

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