Sprintf not working on bluepill

Development Platforms
#1

Hello!

Could someone please help me with sprintf on bluepill?
If i compile with mapel core sprintf works but not with st-core.

Searching on the internet suggests to put “-u _printf_float” into linker flags but it did not compile…

Robert

Here’s my configuration:

main.cpp:

#include <Arduino.h>

char displayString[10];

void setup()
{
    Serial.begin(115200);
} 
void loop()
{
    sprintf(displayString, "%f", 123.4);
    Serial.print(displayString);
    delay(200);
}

platformio.ini:

[env]
platform = ststm32

build_flags =
-D PIO_FRAMEWORK_ARDUINO_ENABLE_CDC
-D USBCON
-D USBD_VID=0x0483
-D USB_MANUFACTURER=“Unknown”
-D USB_PRODUCT="“BLUEPILL_F103C8"”
-D HAL_PCD_MODULE_ENABLED

framework = arduino
board_build.core = st

[env:bluepill]

board = genericSTM32F103CB

Linker error with CONFIG_NET_TCP=y
#2

Exactly, this must be a linker flag, i.e. -Wl, prefixed. Have you tried adding

-Wl,--undefined,_printf_float

as a new line to the build_flags in the platformio.ini?

1 Like
#3

Thank you very much!

I made a mistake with -Wl,-u _printf_float.

Why is that not the default in platformio?

Robert

#4

The default in STM32Duino is also no floating-point printf. It also has to be specially activated. Flash space is precious on these smaller devices. Thus PlatformIO does the same and has maximum compatibility with its behavior.

#5

Thank you very much!