当函数返回指针时，为什么会出现“初始化使指针从整数开始”的问题？

Question

I am making an anagram program that takes a word and finds its anagrams then returns the list of anagrams from a given dictionary file. I am using a linked list as a hash map and a list for each node of the hash map (as per my assignment). I am pretty new to C so I am having a lot of issues with memory and pointers.

Some of the common errors I am getting when I compile: warning: initialization makes pointer from integer without a cast list *pList = getListFromMap(key); I don't understand this one, pList is a list pointer and getListFromMap is returning a list pointer.

conflicting types for getListFromMap() list *getListFromMap(int key) {

previous delcaration of getListFromMap was here getListFromMap(key); I read something about forward declaration? Though I am not sure how this works, I got an error trying it.

 typedef struct list {
     char *word;
     struct list *next;
 } list;

 typedef struct hashmap {
     list *words;
     int key;
     struct hashmap *next;
 } hashmap;

hashmap *pMapHead;
hashmap *pMapCurr;
list *pListHead;
list *pListCurrd;
int sum = 0; // sum of words
int hCount = 0;

void addWordsToMap(int key, list *words) { // create hashmap

    hashmap *pHash = pMapHead;
    pMapCurr = pHash;
    while (pMapCurr) {
            pMapCurr = pMapCurr->next;
    }
    pMapCurr->words = words;
    pMapCurr->key = key;
    pMapCurr->next = NULL;
    hCount += 1;
}


list *addWord(int key) {
    pListHead = getListFromMap(key); 
    pListCurr = pListHead;
    while (pListCurr) {
        pListCurr = pListCurr->next;    
    }
    pList->word = word;
    pList->next = NULL;
    pCurr->next = pList;
    pCurr = pList;

    return pListHead;
}

list *getListFromMap(int key) {
    hashmap *map = pMapHead;
    pMapCurr = map;
    while (pMapCurr != NULL) {
        if (pMapCurr->key == key) {
            return pMapCurr->words;
            free(map);
        }
        pMapCurr = pMapCurr->next;
    }
}

  int getSum(char* word) {
    int sum = 0;
    int i = 0;
    while (word[i]) {
        word[i] = toupper(word[i]);
        sum += word[i] - '@';
        i++;
    }
    return sum;
}

void loadWords() {
    FILE* dict = fopen("/home/akw54/Desktop/CS283/akw54-cs283-            summer2016/A1/dict", "r");
    if (dict == NULL) {
        return;
    }

    pListHead = (list *) malloc(sizeof(pListHead));
    pListCurr = pListHead;
    pMapHead = (hashmap *) malloc(sizeof(pMapHead));
    pMapCurr = pMapHead;
    int key = 0;    
    list wordList;
    char word[128];
    while(fgets(word, sizeof(word), dict) != NULL) {
        key = getSum(word);
        addWordsToMap(key, addWord(key));
    }   
    free(dict);
}

void main() {
    loadWords();
    free(pMapHead);
    free(pMapCurr);
    free(pListHead);
    free(pListCurr);
}

Answer 1

The reason that you get "initialization makes pointer from integer" warning, despite the function returning a pointer, is somewhat obscure. The root case is that the function has no prototype, but that's not the whole story. According to pre-C99 rules, you were allowed to call a function that has no forward declaration, but the compiler must assume that all parameters are subject to default type promotions , and the return type is int as well.

That is why when the compiler sees pListHead = getListFromMap(key) call, it assumes that the function returns an int . In order to avoid this problem, add a forward declaration at the top of the file, right after the typedef s:

list *getListFromMap(int key);