How do I initialize a Priority Queue (custom made library) - c

Question

So for this project, we are required to check if words are palindromes by looking down a stack and forwards through a queue. I have all the logic together, as well as the #include in my palindrome.c file. All I'm having trouble with is defining it correctly while using (allocPQueue seen below) in my palindrome checking method.
Here is an excerpt the .c for PriorityQueue
#include "PriorityQueue.h"
PQueue* allocPQueue(uint elementSize, PQMode mode){
PQueue* pq = (PQueue*)calloc(1, sizeof(PQueue));
pq->elements = allocDList(elementSize, NULL, NULL);
//the elementSampling is to speed up search time, but it is not yet ready
//in order for it to work I cannot make a copy of DNode*, rather I should
//place the pointer of a DNode directly into the array
//I will call this a DeepDArray
pq->elementSampling = (GenericArray)allocDArray(10, sizeof(DNode*));
pq->mode = mode;
if(mode == PQMODE_STACK){
pq->priorityExtractor = &stackPriority;
}
else if(mode == PQMODE_QUEUE){
pq->priorityExtractor = &queuePriority;
}
return pq;
}
void releasePQueue(PQueue* pq){
if(pq){
if(pq->elements){
releaseDList(pq->elements);
}
if(pq->elementSampling){
releaseDArray(pq->elementSampling);
}
free(pq);
}
}
Object peekMin(PQueue* pq){
if(isEmptyPQueue(pq)){
return NULL;
}
Object data = malloc(pq->elements->elementSize);
memcpy(data, pq->elements->head->data, pq->elements->elementSize);
return data;
}
Here is the code in my palindrome.c file (excluding inclusions):
#include "PriorityQueue.h"
bool isPalindrome(char* str, uint length);
char getPalindromeChar(char c);
PQueue* stack;
PQueue* queue;
int main(int argc, char** argv){
if(isPalindrome(argv[1], strlen(argv[1]))){
printf("%s is a palindrome\n", argv[1]);
}
else{
printf("%s is not a palindrome\n", argv[1]);
}
return 0;
}
bool isPalindrome(char* str, uint length){
//TODO
//insert your check, you are only allowed to use a Stack, a Queue, and the char
//getPalindromeChar(char) helper function
char ch;
int wordLength;
int counter;
char stackChar;
char queueChar;
bool stillPalli;
stack = allocPQueue(sizeof(char), PQMODE_STACK); <--"undefined reference to 'allocPQueue'"
queue = allocPQueue(sizeof(char), PQMODE_QUEUE); <--"undefined reference to 'allocPQueue'"
wordLength = 0;
int i;
for(i = 0; i < length; i++){ // Goes through the str array, looking char-by-char for
ch = str[i];
ch = getPalindromeChar(ch);
wordLength++;
// places them in stack and queue
add(stack,ch);
add(queue,ch);
}
stillPalli = true;
while(stillPalli && (counter < wordLength)){
stackChar = top(stack);
pop(stack);
queueChar = front(queue);
dequeue(queue);
// test for equality
if(strcmp(stackChar, queueChar) != 0){
stillPalli = false;
}
counter++;
}
}

Answer 1

Declare your function allocPQueue() inside PriorityQueue.h:
extern PQueue* allocPQueue(uint elementSize, PQMode mode);
When compiling your palindrome.c the compiler needs to know that there is, somewhere, a function that will be available at link time.
The extern keyword does exactly this: it populates the compiler symbol table but don't try to define the actual contents (the assembly code, in the case of a function) of it. The compiler will output the object code (palindrome.o) with annotations that this function still lacks a definition. It will come from another object file.
Then enters the linker. You should pass both palindrome.o and PriorityQueue.o, so that no reference goes undefined on the final executable file.