What is RONG that I am doing with sprintf() function?

[GolamMostafa]

I have wished to convert a float number (say: 23.7) into a string using NANO/UNO and sprintf() function; but, I am not getting the correct values. The Serial.println(myData[0], HEX); shows 0x3F instead of 0x32. Would appreciate to have my mistake/ignorance being pointed.

sketch:

char myData[5];

void setup()
{
  Serial.begin(9600);
  float myTemp = 23.7;
  sprintf(myData, "%.1f", myTemp);
  Serial.println(myData[0], HEX);    // shows: 3F instead of 32
}

void loop(){}

[J-M-L]

On which arduino?

[GolamMostafa]

Arduino NANO/UNO.

[J-M-L]

It’s not implemented. (For Floating point types). Try on an ESP32 it will work
(Or use dtostrf( ) avr-libc: <stdlib.h>: General utilities)

[johnwasser]

It's an AVR run-time library thing, not an Arduino thing.

https://www.nongnu.org/avr-libc/user-manual/group__avr__stdio.html#gaa3b98c0d17b35642c0f3e4649092b9f1

If the full functionality including the floating point conversions is required, the following [linker] options should be used:

-Wl,-u,[vfprintf] -lprintf_flt -lm

[GolamMostafa]

It works well with both ESP8266 NodeMCU and DUE.

Thanks for the information which I know now.

[GolamMostafa]

@johnwasser

-Wl,-u,[vfprintf] -lprintf_flt -lm

Where to put in the UNO code? Any example?

[J-M-L]

it's not in the UNO code, you would need to modify the compilation (linker step) flags used by the IDE. this is not a simple preference to change in the IDE... (I think you need to explore creating a compiler.cpp.extra_flags property in a local file like platform.local.txt... Not sure about the details, read about this some time ago)

[J-M-L]

found this:

Additional compiler options

pert: You might be interested to know about this nice feature: Arduino IDE 1.5 3rd party Hardware specification · arduino/Arduino Wiki · GitHub rather than modifying platform.txt directly, you can instead define the compiler.cpp.extra_flags property in a file named platform.local.txt that you place in the same folder as platform.txt. The property definitions in platform.local.txt override those in platform.txt. This is convenient because every time you update to a new version of the hardware…

[oqibidipo]

Just choose it from the menu:

Oh yeah, you need to add this to boards.local.txt first:

menu.printf=AVR printf Version
menu.scanf=AVR scanf Version

uno.printf=default
uno.menu.printf.default=Default printf
uno.menu.printf.default.avr_printf_flags=
uno.menu.printf.full=Full printf
uno.menu.printf.full.avr_printf_flags=-Wl,-u,vfprintf -lprintf_flt
uno.menu.printf.minimal=Minimal printf
uno.menu.printf.minimal.avr_printf_flags=-Wl,-u,vfprintf -lprintf_min
uno.scanf=default
uno.menu.scanf.default=Default scanf
uno.menu.scanf.default.avr_scanf_flags=
uno.menu.scanf.full=Full scanf
uno.menu.scanf.full.avr_scanf_flags=-Wl,-u,vfscanf -lscanf_flt
uno.menu.scanf.minimal=Minimal scanf
uno.menu.scanf.minimal.avr_scanf_flags=-Wl,-u,vfscanf -lscanf_min
uno.compiler.c.elf.extra_flags={avr_printf_flags} {avr_scanf_flags}

nano.printf=default
nano.menu.printf.default=Default printf
nano.menu.printf.default.avr_printf_flags=
nano.menu.printf.full=Full printf
nano.menu.printf.full.avr_printf_flags=-Wl,-u,vfprintf -lprintf_flt
nano.menu.printf.minimal=Minimal printf
nano.menu.printf.minimal.avr_printf_flags=-Wl,-u,vfprintf -lprintf_min
nano.scanf=default
nano.menu.scanf.default=Default scanf
nano.menu.scanf.default.avr_scanf_flags=
nano.menu.scanf.full=Full scanf
nano.menu.scanf.full.avr_scanf_flags=-Wl,-u,vfscanf -lscanf_flt
nano.menu.scanf.minimal=Minimal scanf
nano.menu.scanf.minimal.avr_scanf_flags=-Wl,-u,vfscanf -lscanf_min
nano.compiler.c.elf.extra_flags={avr_printf_flags} {avr_scanf_flags}

That's for Uno and Nano, you have to add similar lines for ech board you want to use.

[J-M-L]

cool stuff

[GolamMostafa]

@oqibidipo

boards.local.txt

Where should I look for that file in my PC -- I mean the location path? I have made a search in my PC; it is apparently not found!

[sterretje]

I guess that you need to create it if it does not exists. Search for boards.txt and pick the directory that is the most recent. Either in C:\Program Files (x86)\Arduino\hardware\arduino\avr if you never updated the AVR boards package or in a subdirectory of C:\Users\YourUsername\AppData\Local\Arduino15\packages\arduino\hardware\avr\version if you did update it.

[david_2018]

There is also the dtostrf() function for converting a float to a char array.
You can also print the float directly, if you do not need the string elsewhere.

[GolamMostafa]

Unfortunately, the file does not exit in my PC. I have looked in both the paths you have referred

[sterretje]

@GolamMostafa

Unfortunately, the file does not exit in my PC.

You missed the below from my original reply (emphasis added).

@sterretje

I guess that you need to create it if it does not exists.