如何将uint32_t转换为double或float和print？

Question

I'm using an analog to digital converter to read a voltage value from 0 to 3.3V. The ADC gives an output from 0x00 to 0x0FFF (0 to 4095). I want to print the voltage reading with two decimal places. I have read a number of answers but nothing I've tried has worked. Here's my code:

uint32_t pui32ADC0Value[1]; // ADC0 data value
double D0v;                 // Decimal value

// Read value from ADC
ADCSequenceDataGet(ADC0_BASE, 3, pui32ADC0Value);

// Convert to decimal
D0v = (double)pui32ADC0Value[0] / 4095 * 3.3;

// Print to console
UART0printf("\n\r> D0 = %.2d V", D0v);

The output I get is: D0 = ERROR2d V

pui32ADC0Value prints without any problems and gives the expected values, so I know that it is working.

What does this error mean?

NOTE: UART0printf is a pre-defined UART function on the TIVA TM4C microcontroller I am using.

UPDATE: I wrongly assumed UART0printf is identical to printf , as I have used it before with %u , %s , and %x . However for numbers it only supports %c , %i , and %u . I am re-working my code and will update if I don't get anywhere.

UPDATE 2: Could I do something like this? I know it will round incorrectly...

uint32_t pui32ADC0Value[1]; // ADC0 data value
uint32_t D0v[2];                 // Decimal value

// Read value from ADC
ADCSequenceDataGet(ADC0_BASE, 3, pui32ADC0Value);

// Convert to decimal
for ( int i = 0; i <= 2; i++){
    D0v[i] = (pui32ADC0Value[0]/10^i) / 4096 * 3.3;
}

// Display the AIN0 (PE0) digital value on the console.
UART0printf("\n\r> D0 = %d.%d%d V", D0v[0],D0v[1],D0v[2]);

Answer 1

If this function works printf like:

UART0printf("\n\r> D0 = %.2f V\n", D0v);

Also your code may work a little faster if you use:

D0v = (double)pui32ADC0Value[0] * (3.3 / 4095);

The compiler will precompute 3.3 / 4095 and will do a single floating point multiply operation. Otherwise it's possible that the division is done first (which usually takes much more CPU cycles than a multiply) and then the multiply * 3.3 will be done.

Also since you seems to need only 2 digit precision, you could use float (single precision) instead of double . It may execute faster (but it's possible to be even slower), this depends on the platform.

Update for UPDATE2 in the question:

Try this:

uint32_t pui32ADC0Value[1]; // ADC0 data value
uint32_t D0v;               // Decimal value

// Read value from ADC
ADCSequenceDataGet(ADC0_BASE, 3, pui32ADC0Value);

// Convert to millivolts
D0v = pui32ADC0Value[0] * (3300.0 / 4095);

// Display the AIN0 (PE0) digital value on the console.
UART0printf("\n\r> D0 = %d mV", D0v); // If it's OK for you to display in mV
UART0printf("\n\r> D0 = %d.%03d V", D0v / 1000, D0v % 1000); // Print in V

Answer 2

There is no such printf format string as

%.2d

The formatter %d means integer , so there are no decimal-precision options for it. The %. is being parsed as an error (as it does not exist), and the 2d is making it verbatim into your output.

The formatter for floating-point values is %f , so:

%.2f

However, all this is based on the assumption that UART0printf , which you do not identify in your question whatsoever, is identical to printf .