Proper way to use scanf with uint8_t

[yabool2001]

What is the best way to use sscanf with uint8_t?

When I use:

  uint8_t x ;
  char* y = "23" ;
  sscanf ( y , "%hhu" , &x ) ;

I stuck at: 

void HardFault_Handler(void)

I found following workaround that works:

  uint16_t x1 ;
  uint8_t x2 ;
  const char* y = "23" ;
  sscanf ( y , "%hu" , &x1 ) ;
  x2 = (uint8_t) x1 ;

but it doesn't look best. So what is the right way of processing uint8_t in above case?

V/r

yabool2001

[AScha.3]

just guessing:  you search for a 3-char sequence in a 2-char string - what should happen ? 

telling you, oh, you doing wrong, look here... it tries.

make your string some 50 chars long, then search 3-char sequence there... 🙂

+ if x is defined as int16 , you cannot use a int8 as target.

[TDK]

If it's implemented, it's this:

#include <inttypes.h>

...

    sscanf(y, "%" SCNu8, &x);

[Pavel A.]

This looks like limitation of newlib-nano (no ll and no hh). Your workaround is perfect.

[Tesla DeLorean]

Always inter-staged via an int as this can be problematic on several platforms.

[yabool2001]

I've implemented it:

#include <stdio.h>
#include <inttypes.h>

uint8_t x ;
char* y = "23" ;
sscanf ( y , SCNu8 , &x ) ;

and it doesn't work:

17:11:02 **** Incremental Build of configuration Debug for project Test_uint8_t_in_sscanf ****
make -j8 all 
arm-none-eabi-gcc "../Core/Src/main.c" -mcpu=cortex-m0plus -std=gnu11 -g3 -DDEBUG -DUSE_HAL_DRIVER -DSTM32G071xx -c -I../Core/Inc -I../Drivers/STM32G0xx_HAL_Driver/Inc -I../Drivers/STM32G0xx_HAL_Driver/Inc/Legacy -I../Drivers/CMSIS/Device/ST/STM32G0xx/Include -I../Drivers/CMSIS/Include -O0 -ffunction-sections -fdata-sections -Wall -fstack-usage -fcyclomatic-complexity -MMD -MP -MF"Core/Src/main.d" -MT"Core/Src/main.o" --specs=nano.specs -mfloat-abi=soft -mthumb -o "Core/Src/main.o"
../Core/Src/main.c: In function 'main':
../Core/Src/main.c:96:16: error: 'SCNu8' undeclared (first use in this function)
   96 |   sscanf ( y , SCNu8 , &x ) ;
      |                ^~~~~
../Core/Src/main.c:26:1: note: 'SCNu8' is defined in header '<inttypes.h>'; did you forget to '#include <inttypes.h>'?
   25 | #include <inttypes.h>
  +++ |+#include <inttypes.h>
   26 | 
../Core/Src/main.c:96:16: note: each undeclared identifier is reported only once for each function it appears in
   96 |   sscanf ( y , SCNu8 , &x ) ;
      |                ^~~~~
make: *** [Core/Src/subdir.mk:34: Core/Src/main.o] Error 1
"make -j8 all" terminated with exit code 2. Build might be incomplete.

17:11:02 Build Failed. 2 errors, 0 warnings. (took 645ms)

 whole project is available here: Test_uint8_t_in_sscanf (github.com)

V/r

yabool2001

[yabool2001]

Hi Tesla,

thanks for interacting. As you see I've already proposed similar workaround.

I'm looking for  better and simple solution.

[TDK · Accepted solution]

Then it's not implemented in the library you're using (nano).

You can link to the standard C++ library and it's likely in there.

[yabool2001]

Thanks a lot.

[yabool2001]

Hi,

I was expecting to get x = 23 after following code:

  uint8_t x ;
  char* y = "23" ;
  sscanf ( y , SCNu8 , &x ) ;

but I got always x = 32 regardless of the value in string.