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uvision 5 : can not printf "float"

Fausto Bartra

I am working with the C8051F580 using a custom board.

I use UART0 to communicate with TERATERM. 115200 bps

I am using printf to send characters to TERATERM

for decimal printing works fine: printf ("%d",(samples[i]*5)/100);

but if I change it to float it displays "???" : printf ("%3.6f",(samples[i]*5)/100);

"samples" is unsigned int

any suggestion will be appreciated

Thank you.

Fausto Bartra

  • +1

    Try: printf ("%3.6f", (samples[i] * 5.0) / 100.0);

    or, depending on the expected range of "samples": printf ("%3.6f", (samples[i] * 5) / 100.0);

  • 0 in reply to Rene Koenig

    Rene:

    this works now, thank you.

    it is funny that you need to have "5 & 100" written as "5.0 & 100.0" for the compiler to work.

    Thanks very much

    Fausto

  • 0 in reply to Fausto Bartra

    That's not so much "funny" as it is the way C works, and always did: operations on integers yield integers, so if it's floating-point output you wanted, you have to transition to floating-point at some point in the computation.

    It may well be a generally better plan to not involve floats at all, though, and instead allow the output to come without that decimal separator:

    printf("%9u", samples[i]*5);

    because surely, whatever is at the receiving end of that output has an easier time converting to floating-point data formats than a small, FPU-less 8051 derivative.