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Assignement binary value to a variable dosn't work

nico23
Associate III

As title suggest.

If I do

int my_var;
my_var = 0b01;

 my_var stays 0

Instead with

int my_var;
my_var = 0x01;

Everything works

 

STM32CubeIDE

Version: 1.14.1

Build: 20064_20240111_1413 (UTC)

15 REPLIES 15
Andrew Neil
Chief III

Do you get any warnings/errors ?

Binary literals aren't part of the C standard - only available by extension - so are you sure it's valid for the language spec you're using?

CORRECTION

Binary literals were introduced in C23:

https://queue.acm.org/detail.cfm?id=3588242#:~:text=C23%20understands%20binary%20literals%20and,binary%20(%2201010101%22).

So they are very new!

STTwo-32
ST Employee

Hello @nico23 

I've personally tested using the STM32WB55-NUCLEO and the STM32CubeIDE V1.14.1 and this simple code:

  /* USER CODE BEGIN 1 */
	int my_var;
	__NOP();
	my_var = 0b01;
  /* USER CODE END 1 */

And that works fine (even without the __NOP() ) and set the my_var to 1 as you can see: 

STTwo32_0-1708534413008.png

Could you give more details about your issue.

Best Regards.

STTwo-32

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SofLit
ST Employee

And if you add volatile to your declaration :

volatile int my_var;?

 

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That might not help prevent it from being optimized.

Memory inspection only works if the value is in memory, not in registers.

Get printf() / STDIO plumbing working, and printf() the value, or sprintf() via HAL_UART_Transmit()

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Still, likely to be exceedingly non-portable..

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Memory inspection only works if the value is in memory, not in registers.


Indeed, but in the current case the variable and its affectation is in the memory. 

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@SofLit wrote:

Indeed, but in the current case the variable and its affectation is in the memory. 


Well, in your test they were - we can't tell what happened in the OP's case ...

@nico23 - you need to provide a minimum but complete example which illustrates the issue.

Contextually its not presented well enough.

Could be an auto/local variable, which might mean it's held in a register or on the stack.

If it's not throwing a syntax error on compilation I'd assume one hurdle has been jumped. Looking at a disassemble or listing file might give an idea about what is / is not happing.

Not clear how it's being viewed, or how the determination is made it has the wrong value in reality.

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TDK
Guru

There is no chance the compiler is not handling this correctly. Likely to be you misinterpreting the data. Not enough information presented to reproduce or even verify the claim.

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