C Pointer becomes NULL in a loop

I found many questions "pointer becomes NULL", but struggling to apply the answers to my problem.

I have 3 nested structures. Struct A

must contain an array struct B

, which contains one structure C

, which itself must contain an array int

:

typedef struct {
    int32_t *data;
    uint16_t nData;
    uint16_t dataOffset;        
} Window;

typdef struct {
    Window *window;
    const char *datasetPath;
} Dataset

typedef struct {
    char *id;
    uint8_t count;
    Dataset *datasets;
} DatasetGroup;

      

        
        
        
      

    

I have a function new

for structs:

int8_t dataset_new(Dataset *ds, const char *datasetPath, uint16_t winSize){
    ds->datasetPath = datasetPath;
    ds->window = malloc(sizeof(*(ds->window));
    ds->window->data = malloc(sizeof(int32_t) * (winSize));
    return 0;

int8_t datasetgroup_new(DatasetGroup *dg, char *id){
    dg->id = id;
    dg->count = 0;
    dg->datasets = malloc(sizeof(*(dg->datasets)) * 255);
}

      

        
        
        
      

    

And I have a function add

to add Dataset

to DatasetGroup

:

int8_t datasetgroup_add(DatasetGroup *dg, const char *filePath, uint16_t winSize){
       // Create the dataset
       Dataset ds; 
       dataset_new(&ds, filePath, winSize);

       // Add the dataset to the dataset array
       dg->datasets[dg->count] = ds;
       dg->count++;
       return 0;
       }

      

        
        
        
      

    

Then I iterate over the data through the dataset to populate the data, doing things like:

     for (i = 0 ; i < datasetCount ; i++){
         Dataset *ds = &(dg->datasets[i])

      

        
        
        
      

    

Always in the second introduction the array data

becomes a null pointer: data = ds-> window-> data p>

I understand that I did something wrong by missing pointers (?), But I'm not sure what exactly I did wrong ....