trying to insert data with pointer to struct causing a segmentation fault - c

Question

while I was trying to implement my own (string type) Map, I ran into a problem that causes a segmantation fault, while trying to put data in the "value" corresponds to the key Im trying to update.
this is the declaration of the structs, the map struct is an abstract one, so its pointer is in the header file:
typedef struct KeyValue {
char* key;
char* value;
} *keyValue;
struct Map_t {
keyValue* elements;
int size;
int max_size;
int iterator;
};
this is the function that allocates the memory for all the elements inside the map, and initializing them:
Map mapCreate() {
Map map = malloc(sizeof(*map));
if (map == NULL) {
return NULL;
}
map->elements = malloc(INITIAL_SIZE * sizeof(keyValue));
if (map->elements == NULL) {
free(map);
return NULL;
}
map->size = 0;
map->max_size = INITIAL_SIZE;
map->iterator = 0;
return map;
}
this is the function that put an element to a key - override it if there is already an existing key, or making a new one if needed:
MapResult mapPut(Map map, const char* key, const char* data) {
if (map == NULL || key == NULL || data == NULL) {
return MAP_NULL_ARGUMENT;
}
int index = mapFind(map,key);
char* tmp_key = copyString(key); //making a copy of the const key
char* tmp_value = copyString(data); //making a copy of the const data
if (index != ELEMENT_NOT_FOUND) {
keyValue element = map->elements[index];
element->value = tmp_value; //assigning the requested data to the value corresponds to the key
free(tmp_value);
free(tmp_key);
return MAP_SUCCESS;
}
if (map->size == map->max_size) {
if (expand(map) == MAP_OUT_OF_MEMORY) {
return MAP_OUT_OF_MEMORY;
}
}
return createKeyValue(map, tmp_key ,tmp_value); //creates a new key-value
}
and this is the createKeyValue function:
static MapResult createKeyValue(Map map, char* tmp_key, char* tmp_value) {
// we use this function inside another one that checks for null arguments
assert(map != NULL);
if (tmp_key == NULL || tmp_value == NULL) {
return MAP_OUT_OF_MEMORY;
}
int index = map->size;
keyValue element = map->elements[index];
strcpy(element->key,tmp_key); // segmantation fault here
strcpy(element->value,tmp_value);
free(tmp_key);
free(tmp_value);
map->size++;
return MAP_SUCCESS;
}
Im getting the segmentation fault while this function is trying to access with the strcpy function. I already checked if I allocated memorry correctly, and to me it seems that I did everything I should do.
Im really lost because for 2 days I tried everything and cant find the solution.

Answer 1

You have many problems, some of which are listed in comments.
But the root cause seems to be that you don't actually allocate memory for the struct KeyValue structure objects. That means map->elements[index] will be an indeterminate and invalid pointer, for all possible indexes.
You need to allocate memory for map->elements[index].
A possibly fixed version of the createKeyValue function could look something like:
static MapResult createKeyValue(Map map, char* tmp_key, char* tmp_value) {
// we use this function inside another one that checks for null arguments
assert(map != NULL);
if (tmp_key == NULL || tmp_value == NULL) {
return MAP_OUT_OF_MEMORY;
}
int index = map->size;
// Allocate memory for the structure
map->elements[index] = malloc(sizeof map->elements[index]);
// Make the key and value pointers point to the newly allocated "temporary" strings
map->elements[index]->key = tmp_key;
map->elements[index]->value = tmp_value;
map->size++;
return MAP_SUCCESS;
}