Dynamic memory reallocation for a static array field of a structure

Question

Consider the following structures:

// A simple structure to hold some information 
struct A {
    unsigned long id; 
    char title[100]; 
};

// A simple database for storing records of B
struct B {
    unsigned int tableSize; // Total available space in the 'table' field (initially, set to 5)
    unsigned int entriesUsed; // Number of used entries of the 'table' field
    struct A table[5]; 
};

Is it correct to assume that the realloc function (line 5 below) in the following code increases the size of the table field correctly despite the fact that it is defined as a static array?

void add(struct B* db, struct A* newEntry)
{
    if (db->entriesUsed >= db->tableSize) {
        // Does the following line increase the size of 'table' correctly?
        db = (struct B*)realloc(db, sizeof(db) + 5*sizeof(struct A));
        db->rowsTotal += 5;
    }

    db->table[db->entriesUsed].id = newEntry->id;
    memcpy(db->table[db->entriesUsed].title, table->title, sizeof(newEntry->title));

    db->entriesUsed++;
}

Answer 1

No, you cannot assign pointers of any sort to arrays.

In this example you are assigning memory to the struct B pointer that you passed into add. This does nothing to the array sizes contained by that structure.

An implementation of what you're trying to do might look like this:

// A simple structure to hold some information 
struct A {
    unsigned long id; 
    char title[100]; 
};

// A simple database for storing records of B
struct B {
    unsigned int tableSize; // Total available space in the 'table' field (initially, set to 5)
    unsigned int entriesUsed; // Number of used entries of the 'table' field
    struct A *table; 
};

void add(struct B* db, struct A* newEntry)
{
    if (db->entriesUsed >= db->tableSize) {
        // Add 5 more entries to the table
        db->tableSize += 5
        db->table = realloc(sizeof(struct A) * db->tableSize)
    }

    memcpy(&db->table[db->entriesUsed], newEntry, sizeof(struct A));

    db->entriesUsed++;
}