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08-22-2009, 05:23 PM
| #1 |
| Registered User Join Date: Aug 2009
Posts: 11
| Assigning Array Elements By Reference Can you spot an error in my code? It shows no warnings but causes a seg fault. I've isolated it down to the wrd[] lines in red. Rest of the code available if needed. Thanks in advance. Code: char * fetchword( FILE* ifp, char* *wrd, int* wrd_count ) {
unsigned int c ; /*character to be added to end of current string*/
int wrd_len = 0 ; /*number of characters to be in new string*/
/*other stuff done here*/
*wrd = realloc( *wrd, wrd_len * sizeof(char) ) ; /*expand current array by one char*/
if( *wrd == NULL ) {
perror("realloc returned NULL. Unable to allocate memory.") ;
exit (-1) ;
}
*wrd[wrd_len-1] = c ; /*replace existing '\0' with new char*/
*wrd[wrd_len] = '\0' ; /*add the string terminator after new char*/
return *wrd ;
Last edited by bhenderson; 08-22-2009 at 05:26 PM. |
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08-22-2009, 05:32 PM
| #2 |
| and the Hat of Guessing  Join Date: Nov 2007
Posts: 8,740
| If you alloc wrd_len number of elements, *wrd[wrd_len] doesn't exist. |
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08-22-2009, 06:02 PM
| #3 |
| Registered User Join Date: Aug 2009
Posts: 11
| if *wrd[] doesn't exist, what can I use? Thanks |
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08-22-2009, 06:05 PM
| #4 |
| and the Hat of Guessing Join Date: Nov 2007
Posts: 8,740
| I never said *wrd[] didn't exist. I said *wrd[wrd_len] didn't exist. If you ask for six things, and then try to use the seventh, what do you expect? |
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08-22-2009, 06:20 PM
| #5 |
| Registered User Join Date: Aug 2009
Posts: 11
| Oh right, yes, that would be obvious then. Sorry for being dumb! |
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08-23-2009, 02:35 PM
| #6 |
| Registered User Join Date: Aug 2009
Posts: 11
| I'm pulling my hair out with this one now. I thought I had it sorted last night, but seemingly not! Any clues guys? They'd be really appreciated. Code: char * fetchword( FILE* ifp, char* *wrd, int* wrd_count ) {
/*other stuff here*/
*wrd = realloc( *wrd, (wrd_len+1) * sizeof(char) ) ;
*wrd[(wrd_len-1)] = (char)c ; /*seg fault*/
*wrd[(wrd_len)] = '\0' ; /*seg fault*/
/* *wrd[0] = (char)c; */ /*works fine*/
return *wrd ;
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08-23-2009, 03:13 PM
| #7 |
| Registered User Join Date: Oct 2008 Location: TX
Posts: 1,262
| An array and index expression is the same as a pointer and an offset so don't throw 'em into the same mix Code: *wrd[(wrd_len-1)] = (char)c; Last edited by itCbitC; 08-23-2009 at 03:22 PM. |
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08-23-2009, 03:14 PM
| #8 | |
| and the Hat of Guessing Join Date: Nov 2007
Posts: 8,740
| Quote:
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08-23-2009, 03:21 PM
| #9 |
| Registered User Join Date: Aug 2009
Posts: 11
| Thanks tapstop, that makes sense to me and fixes the issue. Hurray! -The array and index are mixed because wrd is a char**. Working Code: Code: (*wrd)[wrd_len-1] = (char)c ; (*wrd)[wrd_len] = '\0' ;  |
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| Tags |
| array, assign, by reference, double, pointer |
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