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POC Having Trouble Resizing a Hash Table
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13052402
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AcceptedAnswerId
13060223
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1
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6
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2012-10-24T15:27:19.543
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0
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2012-10-25T01:22:03.023
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0
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1639615
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2
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1996
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text
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I'll post snippets of the code here which (I think) are relevant to the problem, but I can pastebin if necessary. Probably posting more than enough code already :P My program includes a hash table which needs to double when a certain hash bucket reaches 20 entries. Although I believe the logic to be good, and it compiles like a charm, it throws up a Segmentation Fault. The code runs like a charm when not resizing, but resizing messes things up. Thanks for any help :) Error <pre><code>Program received signal SIGSEGV, Segmentation fault. 0x0000000000401012 in ml_add (ml=0x7fffffffe528, me=0x75a5a0) at mlist.c:74 74 while((cursorNode->next) != NULL){ Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.80.el6_3.5.x86_64 (gdb) backtrace #0 0x0000000000401012 in ml_add (ml=0x7fffffffe528, me=0x75a5a0) at mlist.c:74 #1 0x0000000000401554 in main (argc=1, argv=0x7fffffffe638) at finddupl.c:39 </code></pre> Structure of Hash Table <pre><code>typedef struct bN { //linked list node containing data and next MEntry *nestedEntry; struct bN *next; } bucketNode; typedef struct bL { // bucket as linked list struct bN *first; int bucketSize; } bucket; struct mlist { struct bL *currentTable; //bucket array }; </code></pre> Add Function <pre><code>int ml_add(MList **ml, MEntry *me){ MList *tempList; tempList = *ml; bucketNode *tempNode = (bucketNode *)malloc(sizeof(bucketNode)); tempNode->nestedEntry = me; tempNode->next = NULL; unsigned long currentHash = me_hash(me, tableSize); if((tempList->currentTable[currentHash].bucketSize) == 0) { tempList->currentTable[currentHash].first = tempNode; tempList->currentTable[currentHash].bucketSize = (tempList->currentTable[currentHash].bucketSize) + 1; } else if((tempList->currentTable[currentHash].bucketSize) == 20){ printf("About to resize"); printf("About to resize"); tempList = ml_resize(&tempList, (tableSize * 2)); tableSize = tableSize * 2; ml_add(&tempList,me); } else{ bucketNode *cursorNode; cursorNode = tempList->currentTable[currentHash].first; while((cursorNode->next) != NULL){ cursorNode = cursorNode->next; } cursorNode->next = tempNode; tempList->currentTable[currentHash].bucketSize = (tempList->currentTable[currentHash].bucketSize) + 1; return 1; } return 1; } </code></pre> Resize Function <pre><code>MList *ml_resize(MList **ml, int newSize){ MList *oldList; oldList = *ml; MList *newList; if ((newList = (MList *)malloc(sizeof(MList))) != NULL){ newList->currentTable = (bucket *)malloc(newSize * sizeof(bucket)); int i; for(i = 0; i < newSize; i++){ newList->currentTable[i].first = NULL; newList->currentTable[i].bucketSize = 0; } } int j; for(j = 0; j < tableSize; j++){ bucketNode *cursorNode = oldList->currentTable[j].first; bucketNode *nextNode; while(cursorNode != NULL){ nextNode = cursorNode->next; ml_transfer(&newList, cursorNode, newSize); cursorNode = nextNode; } } free(oldList); return newList; } </code></pre> Transfer to new list function <pre><code>void ml_transfer(MList **ml, bucketNode *insertNode, int newSize){ MList *newList; newList = *ml; bucketNode *tempNode = insertNode; tempNode->next = NULL; unsigned long currentHash = me_hash((tempNode->nestedEntry), newSize); if((newList->currentTable[currentHash].bucketSize) == 0) { newList->currentTable[currentHash].first = tempNode; newList->currentTable[currentHash].bucketSize = (newList->currentTable[currentHash].bucketSize) + 1; } else{ bucketNode *cursorNode; cursorNode = newList->currentTable[currentHash].first; while((cursorNode->next) != NULL){ cursorNode = cursorNode->next; } cursorNode->next = tempNode; newList->currentTable[currentHash].bucketSize = (newList->currentTable[currentHash].bucketSize) + 1; } } </code></pre>
Tags
<c><pointers><hash><segmentation-fault><hashtable>
Title
C Having Trouble Resizing a Hash Table
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1. PO
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1. This table or related slice is empty.
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1. USGeesh_SO
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