函数参数指针数组（C）

Question

in my code I have a array of pointers, where the pointers point to my struct

struct Container *bucket[sizeOfHashMap];

I have a function that will return 1 of these array pointers (eg it may return the pointer at array index 6). As an argument it wants a pointer to this pointer. The function can be seen here:

struct Container* getWhichBucket(char word[], struct Container **bucket[10]){
    int value = 0;
    int i = 0;
    int size = strlen(word);
    int hashIndex = 0;

    for(i =0; i < size; i++){
      value += (int)word[i];
    }

    //size of array is worked out by getting memory that array takes up / a slot
    hashIndex =  value % sizeOfHashMap;
    return *bucket[hashIndex];
}

I call the function like this (where test is an array of characters)

addToBucket(test, getWhichBucket(test, &bucket));

the add to bucket looks like this:

void addToBucket(char word[], container **bucket){
    container *temp = (struct Container*)malloc (sizeof(struct Container));
    strcpy(temp->key, word);
    temp->value = 9001;
    temp->next = *bucket;
    *bucket = temp;

    return;
}

However the compiler issues warnings when I compile the code and when I run it I get a segmentation error . Does anyone know why? The warnings can be seen here:

cw.c: In function ‘main’:
cw.c:86:2: warning: passing argument 2 of ‘getWhichBucket’ from incompatible pointer type [enabled by default]
cw.c:37:19: note: expected ‘struct Container ***’ but argument is of type ‘struct Container * (*)[(long unsigned int)(sizeOfHashMap)]’
cw.c:86:2: warning: passing argument 2 of ‘addToBucket’ from incompatible pointer type [enabled by default]
cw.c:56:6: note: expected ‘struct container **’ but argument is of type ‘struct Container *’

Answer 1

You need to change your declaration of addToBucket from

void addToBucket(char word[], container *bucket)
{ 
    container *temp = (struct Container)malloc (sizeof(struct Container)); 
    strcpy(temp->key, word); 
    temp->value = 9001; 
    temp->next = *bucket; 
    *bucket = temp; 
    return; 
} 

to

void addToBucket(char word[], Container *bucket)
{ 
    Container *temp = malloc (sizeof(struct Container)); 
    strcpy(temp->key, word); 
    temp->value = 9001; 
    temp->next = *bucket; 
    *bucket = temp; 
    return; 
} 

Note the change in case for Container -- case matters in C... container is not the same thing as Container .

Also... note... you should not cast malloc in C .

Answer 2

addToBucket(test, getWhichBucket(test, &bucket));

is passing a

struct Container *(*)[10]

to getWhichBucket . That's the wrong type, as the compiler says.

You can fix the prototype and implementation

struct Container* getWhichBucket(char word[], struct Container *(*bucket)[10]){
    int value = 0;
    int i = 0;
    int size = strlen(word);
    int hashIndex = 0;

    for(i =0; i < size; i++){
      value += (int)word[i];
    }

    //size of array is worked out by getting memory that array takes up / a slot
    hashIndex =  value % sizeOfHashMap;
    return (*bucket)[hashIndex];
}

or change the call, but there's no easy way to get a struct Container **bucket[10] from a struct Container *bucket[10] , so then you'd probably still want to change the type and implementation of getWhichBucket .

Since you're not modifying the bucket argument there, there's no need to pass the address, you can simply pass the struct Container *bucket[10] directly,

struct Container* getWhichBucket(char word[], struct Container *bucket[]){
    int value = 0;
    int i = 0;
    int size = strlen(word);
    int hashIndex = 0;

    for(i =0; i < size; i++){
      value += (int)word[i];
    }

    //size of array is worked out by getting memory that array takes up / a slot
    hashIndex =  value % sizeOfHashMap;
    return bucket[hashIndex];
}

and call

addToBucket(test, getWhichBucket(test, bucket));