C语言 结构体、联合、位段

例如，有一些寄存器，寄存器有一些位，每个位都控制不同的设置，要是想单独设置某一个位的值，用位域就是一个比较好的方法，

位域可以无位域名，这时它只用来作填充或调整位置。无名的位域是不能使用的

比如

union _PWM_AUTO_Register{
long value;
struct {

uint16_t pwm_ofs_auto:8; // Automatically determined offset value
uint16_t :8;
uint16_t pwm_grad_auto:8; // Automatically determined gradient value
}PWM_AUTO_Register;
};

寄存器例子：

 

 第一种方法：如果内存小的话可能造成堆栈溢出

 union _GSTAT_Register
{
      uint32_t value;
      struct GSTAT_Register *GSTAT_Register_bit;
};
  struct GSTAT_Register {

    uint8_t reset:1; // Indicates that the IC has been reset since the last read access to GSTAT
    uint8_t drv_err:1; // Indicates that the driver has been shut down due to overtemperature or short circuit detection since the last read access
    uint8_t uv_cp:1; // Indicates an undervoltage on the charge pump. The driver is disabled in this case.
  };

第二种方法：比第一种占用的更小

 union _GSTAT_Register
 {
       uint32_t value;
      struct  {

           uint8_t reset:1; // Indicates that the IC has been reset since the last read access to GSTAT
           uint8_t drv_err:1; // Indicates that the driver has been shut down due to overtemperature or short circuit detection since the last read access
           uint8_t uv_cp:1; // Indicates an undervoltage on the charge pump. The driver is disabled in this case.
         }GSTAT_Register;
 };

union _GSTAT_Register gstat = {0};//调用先出事化
gstat.GSTAT_Register.reset = 1;
gstat.GSTAT_Register.uv_cp =1;
sendData(GSTAT, gstat.value);

位段在使用中可能是从第零位开始0,1，2,3,4等，也可能是从最高位开始

  union _DCCTRL_Register{
            uint32_t value:24;
            struct  {

               uint16_t dc_time:10, // Upper PWM on time limit for commutation
                                :6,
                           dc_sg:8; // Max. PWM on time for step loss detection using dcStep stallGuard2 in dcStep mode.
             }DCCTRL_Register;
        };

一串数字有6位是空的，可以忽略不写加上“:6”即为跳过6个字段，value总共占24位，可一位位操作

我这台是从零开始。

由于是一位一位操作所得到的数就是二进制数，不需要进制转换，与想传入的十进制数或者十六进制数一致。