How to access data of a "set" defined in a macro in C

Question

In Nordic's SDK there's an ADC driver, in which is defined the following default config struct

/** @brief Macro for setting @ref nrfx_saadc_config_t to default settings. */
#define NRFX_SAADC_DEFAULT_CONFIG                                               \
{                                                                               \
    .resolution         = (nrf_saadc_resolution_t)NRFX_SAADC_CONFIG_RESOLUTION, \
    .oversample         = (nrf_saadc_oversample_t)NRFX_SAADC_CONFIG_OVERSAMPLE, \
    .interrupt_priority = NRFX_SAADC_CONFIG_IRQ_PRIORITY,                       \
    .low_power_mode     = NRFX_SAADC_CONFIG_LP_MODE                             \
}

Now, I want to make clear in my code that I use some default values for the initialization of the ADC. I would like to do this somehow like this:

  static const nrfx_saadc_config_t adc_conf =
  {
      .resolution         = NRF_SAADC_RESOLUTION_12BIT,
      .oversample         = NRF_SAADC_OVERSAMPLE_DISABLED,
      .interrupt_priority = NRFX_SAADC_DEFAULT_CONFIG.interrupt_priority,  // <- THIS LINE
      .low_power_mode     = false
  };

However, this results in the following error:

drv_adc.c(73): error:  #253: expected a ","
        .interrupt_priority = NRFX_SAADC_DEFAULT_CONFIG.interrupt_priority,
drv_adc.c(73): error:  #146: too many initializer values
        .interrupt_priority = NRFX_SAADC_DEFAULT_CONFIG.interrupt_priority,
drv_adc.c(73): error:  #3626: a designator cannot be used with a non-aggregate type "uint8_t"
        .interrupt_priority = NRFX_SAADC_DEFAULT_CONFIG.interrupt_priority,
drv_adc.c: 0 warnings, 3 errors

How do I do this correctly?

Answer 1

1. if adc_conf has static storage duration you cant do this.
2. if adc_conf has automatic storage storage duration (removed static):

  const nrfx_saadc_config_t adc_conf =
  {
      .resolution         = NRF_SAADC_RESOLUTION_12BIT,
      .oversample         = NRF_SAADC_OVERSAMPLE_DISABLED,
      .interrupt_priority = ((nrfx_saadc_config_t)NRFX_SAADC_DEFAULT_CONFIG).interrupt_priority,  // <- it should work
      .low_power_mode     = false
  };

Example: https://godbolt.org/z/GjKnGqT49