how to use float in printf?

[yakabmarci]

Float in printf doesn't seem to work in new projects created in stm32cubeide

If i create a project in sw4stm32 it works, there, it also works if i import the sw4stm32 project, it does not work if i create a new project in cubeide

In all cases the option -u _printf_float is used, but in case of new cubeide project, this setting is somehow ignored and the wrong prinf is included, visible in mapfile

good (imported project):

../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard\libc_nano.a(lib_a-nano-vfprintf_float.o)

bad(new project):

../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard\libc_nano.a(lib_a-printf.o)

[Ozone]

> bad(new project):

> ../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard\libc_nano.a(lib_a-printf.o)

This most probably means you selected a library version without float support in this case.

I'm no CubeIDE user, but such options are usually set while creating the project. Check the IDE documentation/help on how to fix it.

[Knut_Knusper]

Hello,

look at Where can I change the Runtime Library in STM32CubeIDEv1.00

[yakabmarci]

Thanks,

There is not need to repeat what i said, i know that this is the problem, the wrong printf is included even tho I specified that I want the float one with the linker flag -u _printf_float. The -u _printf_float is what is supposed to fix this, and it does for the imported project, but not for the newly generated one

[Ozone]

> There is not need to repeat what i said, ...

It is. as reference to the point I'm referring to.

> The -u _printf_float is what is supposed to fix this, and it does for the imported project, but not for the newly generated one

Perhaps because it referenced another library ? You could compare the sw4stm32 version and the CubeIDE version, to find out.

Check the CubeIDE documentation, as said.

[yakabmarci]

This is so annoying I spent so much time on this.

Now i checked that the right printf is included but it only prints 0.0

The testcode is very simple, just create a standard template project for any stm32 (i tested this stm32f746ng), add code below somewhere

add option "Use float with printf from newlib-nano (-u _printf_float)" in the Tool Settings\MCU Settings

check the buffer via debugger.

any ideas on this?

volatile float a = 3.14f;

char buff[100];

while(1){

 sprintf(buff, "a= %f", a);

a+= 0.001234;

}

stm32ide project -> it only prints a=0.0

sw4stm32 project-> works correctly

[yakabmarci]

what exactly do you mean by the cubeide documentation?

You have any specific one in mind? otherwise this is just trolling, It doesn't work, oh you should check 'the documentation'

I checked many documentations..

[Knut_Knusper]

Did you try the Runtime Library "Standard C" and the option Use float with printf from newlib-nano (-u _printf_float) together?

Because this Setting works at my projekt.

[yakabmarci]

Thanks for the feedback,

I tried newlib (nano.spec) and standard lib, i have the same wrong result in both cases.

But -u _printf_float makes sense only if newlib-nano is used, is it not?

The difference is that the sw4stm32 is a c only project the stm32cubeide is a c++ one (tho only c code is used).

the first one is linked with arm-none-eabi-gcc, the other with arm-none-eabi-g++

I think the problem is in this area somehow, both have the same options, the c++ one has additional options (-lstdc++ -lsupc++)

Edit:

Note: the stm32 project wizard always creates a c++ project, even if i select c project

[Ethan HUANG · Accepted solution]

​Besides enabling -u _printf_float (either by manually typing in MCU GCC Linker/Miscellaneous or checking option in MCU Settings), please modify _estack in linker script for example from 0x2001ffff to 0x20020000 as described in the thread:

https://community.st.com/s/question/0D50X0000AldaPzSQI/cubeide-sprintf-does-not-work-with-f