Struct arrays pointers issue

Question

could somedoby clarify some basic C language moments.

struct key {
    char *name;
    int value;
};

struct key first_key_array[] = {
    {"abc", 5},
    {"xyz", 6},
    {"def", 7}
};

struct key second_key_array[] = {
    {"what", 200},
    {"when", 300}
};

struct data {
    struct key **key_array;
};

struct data all_key_arrays[] = {
    {first_key_array},
    {second_key_array}
};

I could directly access first_key_array[0]:

printf("%s %d", first_key_array[0].name, first_key_array[0].value);

But access via all_key_arrays does not work:

printf("%s %d", all_key_arrays[0].key_array[0].name, all_key_arrays[0].key_array[0].value);

Could somebody share any ideas?

The initializer for struct data all_key_arrays[] = is ill-formed. Your compiler should tell you about this. If you don't see any compiler messages then you need to figure out how to stop disabling your compiler's output messages . You need to fix the compiler messages before trying to run the program. — M.M
– M.M, Commented Mar 2, 2016 at 21:05
The fix will be that struct key **key_array; should be struct key *key_array;, although this design has a problem that if you go in via all_key_arrays then there is no way of checking you don't access past the end of wherever it is pointing — M.M
– M.M, Commented Mar 2, 2016 at 21:06

Jay Elston · Accepted Answer · 2016-03-02 21:07:53Z

1

Try changing the initializer for all_key_arrays to:

struct data all_key_arrays[] = {
    first_key_array,
    second_key_array
};

or

struct data all_key_arrays[] = {
    &first_key_array[0],
    &second_key_array[0]
};

Explanation -- all_key_arrays is an array pointers, so the values you initialize the array to should be, well, pointers.

answered Mar 2, 2016 at 21:07

Jay Elston

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