How to print float values using SEGGER RTT

RE: How to print float values using SEGGER RTT

Sunil Shenoy — Fri, 28 Apr 2017 09:30:47 GMT

@Roger Clark : This method might not yield the right answer if a 0 succeeds the decimal point. Eg: If the number is 3.014, it would print 3.14 while ignoring the 0 after the decimal point.

RE: How to print float values using SEGGER RTT

Roger Clark — Mon, 30 Jan 2017 01:42:16 GMT

If you numbers are in the range that fits in an int (32 bit signed) i.e less than a few billion, then you can just write some simple code to split the number at the decimal point, and print the digits to the left of the point as an integer, then print a "." then print the digits to the right of the point.

e.g.

#define PRECISION 10000
int intPart = (int) floatNumber;
int decimalPart = (floatNumber - intPart) * PRECISION;

prinf("%d.%d",intPart,decimalPart);

This would give you an answer to 4 decimal places

If however your number is something like 1.2345 E-9 then its you will need to pull in a library to handle that sort of complex display

RE: How to print float values using SEGGER RTT

Jan Lundskov — Sun, 29 Jan 2017 14:26:18 GMT

I am using the stdio library. When I look in the stdio.h file I can find the following description:

"Some library variants do not support the \q{f} and \q{F} conversion specifiers in order to reduce code and data space requirements; please ensure that you have selected the correct library in the \b{Printf Floating Point Support} property of the project if you use these conversion specifiers."

It is not described specifcally under the fprintf or printf declaration though.

If I go to the Project Options under Printf/Scanf under the Linker section, then there is an option to set 'Printf Floating Point Supported' to either Yes or No. It is by default set to No.

After setting this option to Yes it works:-)

Thank you so much for your help!

RE: How to print float values using SEGGER RTT

butch — Sun, 29 Jan 2017 10:46:35 GMT

What C library (implementing sprintf()) are you using? You might explore whether the library supports sprintf for float arguments, as in this old thread: www.cypress.com/.../sprintf-bug-psoc-creator-3-5lp-and-format-f. In other words, conversion from float to string by sprintf() might not be implemented in the library, and have a weak definition that does nothing i.e yields an empty string.