Fix: Unsupported use of %f in printf

[MKS-Sean]

Description

When using the arduinoststm32 library (robin nano v3.0), using sprintf_P to copy float variables will make an error, but the test in the maple library is normal (robin nano v2.0)

Tested in MKS Robin nano V3.0 motherboard:
Before modification:

After modification:

Requirements

Use arduinoststm32 library (MKS Robin nano V3.0 mainboard using it).
Use sprintf_P（buf，PSTR（“%.1f”），float_var）;

Benefits

LVGL UI can display float type variable parameters normally

Configurations

default_envs = mks_robin_nano_v3_usb_flash_drive_msc
Configurations.zip

Related Issues

No

[X-Ryl669]

Wouldn't it be easier to set the right linker flags to use the full sprintf version, instead of relying on such painful code?
See here
Basically, it boils down to adding -Wl,-u,vfprintf -lprintf_flt -lm to the linker's command.
Nano v3 is pretty powerful it can support few kB of flash for printing float.

[rhapsodyv]

@MKS-Sean Can you take a look if it's working after Scott reviews?

[thinkyhead]

@X-Ryl669 — For now Marlin is keen to retain Arduino IDE build support, even for code (such as FSMC LCD) that theoretically might never be compiled and run on an AVR.

[thinkyhead]

What would be very useful would be a lightweight C++ string class with operator overrides that would turn our ugly string code into something more elegant. The entire codebase would benefit. I wrote my own C++ string class once many moons ago, but there are probably a million examples around that we could use as a starting-point.

Our only caveat is no dynamic allocation. All buffers must be provided by the caller or allocated on the stack. But, given the ubiquity of "string stuff" it wouldn't be the worst thing to add a dedicated buffer for "current string" work, thus making many function stack frames smaller.