BLE header files

[mehbstnc]

Hello,
I am just trying to uınderstand what is happening in the belown code. It seems like casting pointers but I didnt get the
whole idea.
Can some one explain it ?
Thanks for helps

#define BLE_UUID16_DECLARE(uuid16) \
((ble_uuid_t *) (&(ble_uuid16_t) BLE_UUID16_INIT(uuid16)))

[Craige Hales]

Expand the macros. I think this might be the ones: https://github.com/apache/mynewt-nimble ... ble_uuid.h

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#define BLE_UUID16_INIT(uuid16)         \
    {                                   \
        .u = {                          \
            .type = BLE_UUID_TYPE_16,   \
        },                              \
        .value = (uuid16),              \
    }

so

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(ble_uuid16_t) BLE_UUID16_INIT(uuid16)

means

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(ble_uuid16_t) 
    {                                   \
        .u = {                          \
            .type = BLE_UUID_TYPE_16,   \
        },                              \
        .value = (uuid16),              \
    }

which is an initialized structure. The next bit,

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((ble_uuid_t *) (&

takes the address of the structure and casts it to a more generic structure pointer.

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/** Generic UUID type, to be used only as a pointer */
typedef struct {
    /** Type of the UUID */
    uint8_t type;
} ble_uuid_t;

That in turn is part of a union.

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/** Universal UUID type, to be used for any-UUID static allocation */
typedef union {
    ble_uuid_t u;
    ble_uuid16_t u16;
    ble_uuid32_t u32;
    ble_uuid128_t u128;
} ble_uuid_any_t;

The union has four possible interpretations, depending on the ble_uuid_t at the beginning of each member of the union. The last three all look like

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/** 16-bit UUID */
typedef struct {
    ble_uuid_t u;
    uint16_t value;
} ble_uuid16_t;

which embeds a ble_uuid_t, followed by more data. The first just doesn't have any more data.
I think the extra parens

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(ble_uuid16_t)

are required by the macro to separate ble_uuid16_t from BLE_UUID16_INIT, maybe.

[mehbstnc]

Thank you for your help..