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Proper way to use scanf with uint8_t

yabool2001
Associate III

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

1 ACCEPTED SOLUTION

Accepted Solutions

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.

TDK_1-1698602531295.png

 

If you feel a post has answered your question, please click "Accept as Solution".

View solution in original post

11 REPLIES 11
AScha.3
Chief

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.

If you feel a post has answered your question, please click "Accept as Solution".
TDK
Guru

If it's implemented, it's this:

 

#include <inttypes.h>

...

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

 

 

If you feel a post has answered your question, please click "Accept as Solution".
Pavel A.
Evangelist III

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

 

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

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Up vote any posts that you find helpful, it shows what's working..

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

Hi Tesla,

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

I'm looking for  better and simple 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.

TDK_1-1698602531295.png

 

If you feel a post has answered your question, please click "Accept as Solution".

Thanks a lot.

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.

debug.jpg