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POsingle Queue and multiple Queue using same program not work
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copied!<p>here is two c program to implement queue data structure in simple form</p> <ul> <li><p><em>the first:</em></p> <p>define one queue and it's work perfectly</p></li> <li><p>the second:</p> <p>define multiple queues and it's crash at execution</p></li> </ul> <p>functions are the same in both programs except the <code>main()</code> were the implementation are different little bit.</p> <p>So the question here: why the second code not working?</p> <p><strong>* here is the codes *</strong></p> <p><em>code 1:</em></p> <pre><code>/* Single queue -- this work perfectly */ #include <stdio.h> #define Q_MAX_SIZE 255 struct queue { int* pointer; int* currentValue; int max, count, theQueue[Q_MAX_SIZE]; }; //prototyps void initQueue(struct queue*); unsigned short pushQueue(struct queue*, int); int* popQueue(struct queue*); int main(void) { int j; struct queue q; initQueue(&q); for (j = 0; j < 6; j++) pushQueue(&q, j); int* inputobj = popQueue(&q); while (inputobj != NULL) { printf("%d ", *inputobj); inputobj = popQueue(&q); } printf("\n\ndone..Queue is empty\n"); return 0; } //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ void initQueue(struct queue *Q) { Q->pointer = Q->theQueue; Q->max = Q_MAX_SIZE; Q->count = 0; } unsigned short pushQueue(struct queue *Q, int input) { if (Q->count < Q->max) { *Q->pointer = input; Q->pointer++; Q->count++; return 1; } else return 0; } //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ int* popQueue(struct queue *Q) { int i; if (Q->count > 0) { *Q->currentValue = *Q->theQueue; Q->pointer--; Q->count--; for (i = 0; i < Q->count; i++) { int* currentPtr = Q->theQueue + i; int* nextPtr = currentPtr + 1; *currentPtr = *nextPtr; } return Q->currentValue; } else NULL; } </code></pre> <p><em>code 2:</em></p> <pre><code>/* Multiple queues -- this not work and crash at execution */ #include <stdio.h> #define Q_MAX_SIZE 255 struct queue { int* pointer; int* currentValue; int max, count, theQueue[Q_MAX_SIZE]; }; //prototyps void initQueue(struct queue*); unsigned short pushQueue(struct queue*, int); int* popQueue(struct queue*); int main(void) { int i, j; struct queue obj[5]; for(i=0; i<5; i++) { initQueue(&obj[i]); for(j = 0; j<3; j++) { pushQueue(&obj[i], j); } } for(i=0; i<5; i++) { printf("Queue[%d]:\n", i); int* inputobj; inputobj = popQueue(&obj[i]); while(inputobj != NULL) { printf("Queue[No.%d] = %d\n", i, *inputobj); inputobj = popQueue(&obj[i]); } putchar('\n'); } return 0; } //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ void initQueue(struct queue *Q) { Q->pointer = Q->theQueue; Q->max = Q_MAX_SIZE; Q->count = 0; } unsigned short pushQueue(struct queue *Q, int input) { if (Q->count < Q->max) { *Q->pointer = input; Q->pointer++; Q->count++; return 1; } else return 0; } //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ int* popQueue(struct queue *Q) { int i; if (Q->count > 0) { *Q->currentValue = *Q->theQueue; Q->pointer--; Q->count--; for (i = 0; i < Q->count; i++) { int* currentPtr = Q->theQueue + i; int* nextPtr = currentPtr + 1; *currentPtr = *nextPtr; } return Q->currentValue; } else NULL; } </code></pre> <p><strong>Update:</strong> the problem was in <code>initQueue()</code> and it's solved by allocating memory for <code>Q->currentValue</code> here is the function after editing:</p> <pre><code>void initQueue(struct queue *Q) { Q->currentValue = malloc(sizeof(int)); Q->pointer = Q->theQueue; Q->max = Q_MAX_SIZE; Q->count = 0; } </code></pre>

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