c malloc导致崩溃

Question

Why the 3 malloc above crashes? sometimes they work but only for (globale->dim_schema) > 10 or (globale->dim_schema) >100

struct GLOBALE {

    int dim_schema;
    char *schema;
    int *celle_usate;
    char *punteggi;
    char *percorso_aiuto;
    struct LISTA_SOLUZIONI *soluzioni; 
};

typedef struct GLOBALE *struct_globale;

void modalita_interattiva() {

    int i;
    char lettera;

    char bonus;
    char *parola;
    struct_globale globale;
    globale = malloc(sizeof(struct_globale));

    if(globale == NULL) {

        printf("Impossibile creare struct globale\n");
        exit(EXIT_FAILURE);

    globale->soluzioni = NULL;

    do{
        printf("Quanto grande e' lo schema di ruzzle che vuoi usare? (>0)\n");
        scanf("%d", &(globale->dim_schema));
        printf("Dimensione: %d \n", globale->dim_schema);
    }while(globale->dim_schema<=0);

    globale->celle_usate = malloc(globale->dim_schema * globale->dim_schema * sizeof(int)); <----CRASH
    printf("celle usate\n");
    globale->punteggi = malloc((globale->dim_schema) * (globale->dim_schema) * sizeof(char)); <----CRASH
    printf("punteggi\n");
    globale->schema = malloc(globale->dim_schema * globale->dim_schema * sizeof(char));<----CRASH
    printf("schema\n"); 
...etc etc

Answer 1

This is a good example of why it's not a good idea to hide pointers within a typedef :

globale = malloc(sizeof(struct_globale));

struct_globale is a typedef for struct GLOBALE * . So the above allocation only allocates enough space for a pointer to struct GLOBALE (typically 4 or 8 bytes depending on the machine / compiler). Since the struct is larger than this, you're writing to members that are past the memory offset of the allocated size. This results in undefined behavior.

You need to allocate space for the size of the struct:

globale = malloc(sizeof(struct GLOBALE));

Or alternaltely:

globale = malloc(sizeof(*globale));

Answer 2

The function call

malloc(sizeof(struct_globale))

returns only a region of memory the size of the pointer struct_globale , not the size of the record it refers to. Obviously, memory allocation with malloc and its cousins is rather error prone. However, it can be improved by introducing the following function macros:

#define NEW_ARRAY(ptr, n) (ptr) = malloc((n) * sizeof (ptr)[0])
#define NEW(ptr) NEW_ARRAY((ptr), 1)

With these in place you can simply say

NEW(globale);
NEW_ARRAY(globale->celle_usate, globale->dim_schema * globale->dim_schema);

etc.