This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

How to convert type uint32_t to float??

Hi,
I try to read value of timer of STM32L152VD and convert it to float type. The way I use is first define the below union:

typedef union
{
        uint32_t timercount;
        float    flowtime;
}union_timercount;

union_timercount flow;

then use function below:

uint32_t TIM_GetCounter(TIM_TypeDef* TIMx)
{
  /* Check the parameters */
  assert_param(IS_TIM_ALL_PERIPH(TIMx));

  /* Get the Counter Register value */
  return TIMx->CNT;
}

I send it to serial port:

flow.timercount=TIM_GetCounter(TIM2);
sprintf(str1,"\r\nu=%u f=%f",flow.timercount,flow.flowtime);
uart_out_str(str1);

but what I read is:
u=2248 f=0.000000 why float value is not being converted?

0 Westonsupermare Pier over 9 years ago

The binary representations are different, what do you expect? Go look at how the bits in the 32-bit float split into exponent and mantissa components.

If you want to CONVERT, then use a cast, ie flowtime = (float)timercount
Cancel
Vote up 0 Vote down

Cancel

0 John Linq over 9 years ago in reply to Westonsupermare Pier

#include <stdio.h>
#include <string.h>

// unsigned long long data = 0x4030000000000000;
unsigned long long data = 0x402699999999999A;
double double_value;

unsigned int dat = 2248;  /* added for this case */
float float_val;          /* added for this case */

int main(void)
{
    printf( "double=%d, long long=%d\n", sizeof(double), sizeof(long long) );
    memcpy( &double_value, &data, 8 );
    printf( "double_value = %lf\n", double_value );

    float_val = dat;                          /* added for this case */
    printf( "float_val = %f\n", float_val );  /* added for this case */
}

0 John Linq over 9 years ago in reply to John Linq

#include <stdio.h>
#include <string.h>

// unsigned long long data = 0x4030000000000000;
unsigned long long data = 0x402699999999999A;
double double_value;

int main(void)
{
    printf( "double=%d, long long=%d\n", sizeof(double), sizeof(long long) );
    memcpy( &double_value, &data, 8 );
    printf( "double_value = %.22lf\n", double_value );
}


double=8, long long=8
double_value = 11.3000000000000010000000

Process returned 41 (0x29)   execution time : 0.022 s
Press any key to continue.