wj127 wj127 - 1 month ago 8
C Question

Can someone explain why I get this error with types?

I'm more or less new using pointers in C, so sorry if I make some horrible mistakes! In this case, I'm just trying to copy all the elements of a float vector into another.

I have the following chunk of code inside my main.c file, which works fine:

/* NOTE: hash_list is a global variable*/
void insertDataIntoOurHashList(int dia, int delay, char *aeO, char *aeD){
unsigned int numHash;
ListData *listData;

numHash = getHashValue(aeO);

/* If there's no list yet in this position, then... */
if (hash_list[numHash] == NULL) {
hash_list[numHash] = malloc(sizeof(List));
initList(hash_list[numHash]);
listData = malloc(sizeof(ListData));
listData->key = malloc(sizeof(char*)*strlen(aeD)+1);
strcpy(listData->key, aeD);
listData->key_sec = malloc(sizeof(char*)*strlen(aeO)+1);
strcpy(listData->key_sec, aeO);
listData->numTimes = 1;
listData->retrasos = (float*) malloc(sizeof(float)*7);
listData->retrasos[dia-1] = delay;
insertList(hash_list[numHash], listData);
}
else {
listData = findList2(hash_list[numHash],aeD,aeO);

/* If already exists a data with both equals keys, then... */
if (listData != NULL) {
listData->numTimes++; // We add in one the counter of the list
listData->retrasos[dia-1] = listData->retrasos[dia-1] + delay / 2;
}
/* If exists a data with the same aeD as primary key but not with the aeO as secundary key, then... */
else {
listData = malloc(sizeof(ListData));
listData->key = malloc(sizeof(char*)*strlen(aeD)+1);
strcpy(listData->key, aeD);
listData->key_sec = malloc(sizeof(char*)*strlen(aeO)+1);
strcpy(listData->key_sec, aeO);
listData->numTimes = 1;
listData->retrasos = (float*) malloc(sizeof(float)*7);
listData->retrasos[dia-1] = delay;
insertList(hash_list[numHash], listData);
}
}
free(aeO);
free(aeD);
}


ListData *listData is a pointer that points to a structure defined in my linked-list.h file, and _hash_list_ is a vector of pointers of type List where each one points to a list of type List, defined in the same file:

/**
*
* The TYPE_LIST_KEY is used to define the type of the primary
* key used to index data in the list.
*
*/

#define TYPE_LIST_KEY char*

/**
*
* This structure holds the information to be stored at each list item. Change
* this structure according to your needs. In order to make this library work,
* you also need to adapt the functions compEQ and freeListData. For the
* current implementation the "key" member is used search within the list.
*
*/

typedef struct ListData_ {
// The variable used to index the list has to be called "key".
TYPE_LIST_KEY key;
char *key_sec;
// This is the additional information that will be stored
// within the structure. This additional information is associated
// to the key. You may include any field you may need useful.
float *retrasos;
int numTimes;
} ListData;

/**
*
* The item structure
*
*/

typedef struct ListItem_ {
ListData *data;
struct ListItem_ *next;
} ListItem;

/**
*
* The list structure
*
*/

typedef struct List_ {
int numItems;
ListItem *first;
} List;


Then, back in my main.c file, I loop through every cell in my _hash_list_ , passing the list that pointer of that cell points to, to a function that takes the data from the list and pass them to another function, I mean:

void insertInHash(){
int i;

for(i = 0; i < HASH_SIZE; i++){
if (hash_list[i] != NULL) {
dumpList2(hash_list[i]);
}

}
}

/* This function is called for every cell while looping the hash_list */
void dumpList2(List *l){
ListItem *current;

current = l->first;

while (current != NULL)
{
insertDataIntoOurTree(current->data->key_sec, current->data->key, current->data->retrasos);
current = current->next;
}

}


void insertDataIntoOurTree(char *aeO, char *aeD, float *delays){
List *list;
ListData *listData;
int i;

/* Case when the node exists! */
if (treeData != NULL) {
treeData->num++; // We add in one the counter of treeData
listData = findList(treeData->list, aeD); // We check if the new destination airport is inside the list of the node...

/* If the destination is inside the list... */
if(listData != NULL)
listData->numTimes++; // We add in one the counter of the list

/* If the destination isn't inside... */
else {
/* We create and initialize the new item the list of the node will contain! */
listData = malloc(sizeof(ListData));
listData->key = malloc(sizeof(char*)*strlen(aeD)+1); // Counting with the final '\0' byte!
strcpy(listData->key, aeD); // Remember the case as above with aeO and aeD
listData->numTimes = 1;
listData->retrasos = (float*) malloc(sizeof(float)*7);
//listData->retrasos[dia-1] = delay; // minus one cos we don't want to be out of bound! ;)
//copyDelays(listData->retrasos, delays);
for (i = 0; i < 7; i++) {
listData->retrasos[i] = 0.0;
}
copyDelays(listData->retrasos, delays);

insertList(treeData->list, listData);
}
}
/* THERE ARE MORE CASES DOWN HERE, BUT THEY DON'T MATTER NOW... */

}


The function copyDelays is defined in my linked-list.c file:

void copyDelays(float *delaysToCopy, float *delays){
int i;

for (i = 0; i < 7; i++) {
if (delaysToCopy[i] == 0.0) {
memcpy(delaysToCopy[i], delays[i], sizeof(float));
}
}
}


And finally, when I try to compile all my files, I get this error that I don't understand:

linked-list.c:234:14: error: passing 'float' to parameter of incompatible type 'const void *'
memcpy(delaysToCopy[i], delays[i], sizeof(float*));
^~~~~~~~~~~~~~~
/usr/include/secure/_string.h:65:59: note: expanded from macro 'memcpy'
__builtin___memcpy_chk (dest, src, len, __darwin_obsz0 (dest))
^~~~
/usr/include/secure/_common.h:38:55: note: expanded from macro '__darwin_obsz0'
#define __darwin_obsz0(object) __builtin_object_size (object, 0)
^~~~~~
1 error generated.
make: *** [linked-list.o] Error 1

Answer

The problem is that the arguments you passed to memcpy() function do not match with the function's signature. memcpy() function signature is as follows: (http://www.cplusplus.com/reference/cstring/memcpy/)

void * memcpy ( void * destination, const void * source, size_t num );

As you see it takes pointers as its first and second arguments, whereas delaysToCopy[i] and delays[i] are not pointers just float.

It should solve your problem if you use ampersand sign to get their addresses, as shown below:

memcpy(&delaysToCopy[i], &delays[i], sizeof(float));
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