String print error in default example

Using Arduino Programming Questions
1

I am running the following example arduino-1.8.12\examples\08.Strings\StringConstructors StringConstructors.ino file. I am programming to an Artemis Apollo 3 mcu provided from sparkfun (lora things plus explorable). For some reason floats will not print right , and i cannot figure out why it is not working. Here is the line of code that is not working:

// using a float and the right decimal places:
  stringOne = String(5.698, 3);
  Serial.println(stringOne);

  // using a float and less decimal places to use rounding:
  stringOne = String(5.698, 2);
  Serial.println(stringOne);

Here is the output on the serial monitor:

%5.3f
%4.2f

I cannot figure out why it is printing the format of the value and not the value itself???

2

The other odd thing is that if i write Serial.println(5.698,9); in the code, that works fine and outputs 5.698000000

3

I suspect a bug in the toolchain for the processor; I however can't straight away find something (e.g. a bug report) on the web.

SparkFun has their own forum (https://forum.sparkfun.com/), it might be useful to ask there as well.

Note:
Your code gives the expected result when compiled for a classic Nano.

4

I tried on an ESP32 and it also gives the expected result.

Could you check what you get from:

// using a float and the right decimal places:
  stringOne = String(5.698, 3);
  Serial.println(stringOne.c_str());

  // using a float and less decimal places to use rounding:
  stringOne = String(5.698, 2);
  Serial.println(stringOne.c_str());

I would suspect the mbedOS and core conflicting in some way (may be some printf replacement stuff )

(never played with Artemis Apollo 3 mcu - so can't say)

5

Do you mean the "SparkFun Edge Development Board - Apollo3 Blue"? Or is it a different "SparkFun Apollo 3" board? I ask because I don't see any Arduino support for the "SparkFun Edge Development Board - Apollo3 Blue".

6

I had assumed one of these boards Artemis - SparkFun Electronics

7

It is this board:

8

I tried your code and got the same results:
%5.3f
%4.2f

9

OK so it sounds like String(5.698, 3) returns "%5.3f"
that's really weird....

did you raise a question on sparkFun's forum or GitHub?

10

Not yet, i did a bunch of researching and found these references:

Sounds like that is my exact issue, Do you know where i need to make the change ("platform.minimal-printf-enable-floating-point": true) ?

I found mbed_app.json filename in multiple directories. I am guessing this is the correct one, however adding the line did not seem to work?
\AppData\Local\Arduino15\packages\SparkFun\hardware\apollo3\2.0.5\cores\mbed-os\tools\test\config\app_override_libs

11

The first one seems to be your issue. As I don’t have that platform, unfortunately I don’t know what they refer to…

12

Well i tried a bunch of changes to compiler flags e.g. adding --specs=nano.specs -u _printf_float , turnning off optimization etc. However it does not seem that the libraries are being recompiled with these changes, as the output says this during compilation:

Using previously compiled file:
C"\ .......\AppData\Local\Temp\arduino_build_441533\core\mbed-bridge\core-api\api\Print.cpp.o

Is there a way to force recompilation of the libraries?

13

Here are my flags in .c-flags

-c -std=gnu11 -DMBED_MINIMAL_PRINTF -DMBED_TRAP_ERRORS_ENABLED=1 -O0 -fdata-sections -ffunction-sections -fmessage-length=0 -fno-exceptions -fomit-frame-pointer -funsigned-char -g -mcpu=cortex-m4 -mfloat-abi=softfp -mfpu=fpv4-sp-d16 -mthumb --specs=nano.specs -u _printf_float

14

Also here is what the .ld-flags are, do you know what flag -wl means? Maybe that is causing the issue?

-DMBED_BOOT_STACK_SIZE=1024 -DXIP_ENABLE=0 -Wl,--gc-sections -Wl,--wrap,_calloc_r -Wl,--wrap,_memalign_r -Wl,--wrap,atexit -Wl,--wrap,exit -Wl,--wrap,fprintf -Wl,--wrap,main -Wl,--wrap,printf -Wl,--wrap,snprintf -Wl,--wrap,sprintf -Wl,--wrap,vfprintf -Wl,--wrap,vprintf -Wl,--wrap,vsnprintf -Wl,--wrap,vsprintf -Wl,-n -mcpu=cortex-m4 -mfloat-abi=softfp -mfpu=fpv4-sp-d16 -mthumb --specs=nano.specs -u _printf_float

15

Close the IDE, open it again and load / compile your sketch.

16

Yea it is recompiling it still getting the same result. Not sure what is going wrong. ive added the -u _printf_float to the compiler ld flags, and have also tried deleting nano.specs all together and get the same result

17

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