access uino variable when union name is not defined

Question

I am working with esp32 and trying to use the i2c library.

There is a config struct.

typedef struct{
i2c_mode_t mode;     /*!< I2C mode */
int sda_io_num;      /*!< GPIO number for I2C sda signal */
int scl_io_num;      /*!< GPIO number for I2C scl signal */
bool sda_pullup_en;  /*!< Internal GPIO pull mode for I2C sda signal*/
bool scl_pullup_en;  /*!< Internal GPIO pull mode for I2C scl signal*/

union {
    struct {
        uint32_t clk_speed;     /*!< I2C clock frequency for master mode, (no higher than 1MHz for now) */
    } master;
    struct {
        uint8_t addr_10bit_en;  /*!< I2C 10bit address mode enable for slave mode */
        uint16_t slave_addr;    /*!< I2C address for slave mode */
    } slave;
};
} i2c_config_t;

From this when i try to create and assign in my code the i2c_config_t like:

                i2c_config_t i2cConfigT={
                    .mode = I2C_MODE_MASTER,
                    .sda_io_num = _sda,
                    .scl_io_num = _clk,
                    .sda_pullup_en = GPIO_PULLUP_ENABLE,
                    .scl_pullup_en = GPIO_PULLUP_ENABLE,
                    .master.clk_speed = 100000};

i get error on last row at the . before the master variable.

Error says

expected primary-expression before '.' token

From this i see that there is no defined name for the union is it possible this to be the issue?

What are you using to compile this code? With gcc 11.1.1 it seems to compile without any errors. — larsks, Jul 25 '21 at 14:54
"cStandard": "c11","cppStandard": "c++17", but it is xtensa-esp32-elf compiler from esp-idf framework. it is esp32 project — kyrpav, Jul 25 '21 at 14:59
try giving the `union` a name within `i2c_config_t` , say for example `options` and initialize with `.options.master.clk_speed = 100000` But do you really need the union? you could just make `master` and `slave` as `struct`s within `i2c_config_t` without a huge space hit. — infixed, Jul 25 '21 at 15:21
Where is that error? Which dot does expect the primary-expression ? — CiaPan, Jul 25 '21 at 17:12

score 1 · Accepted Answer · answered Jul 29 '21 at 13:00

1

.master = {
  .clk_speed = 100000,
}

answered Jul 29 '21 at 13:00

kyrpav

756
1
13
43

access uino variable when union name is not defined

1 Answers1