Function pointers that call one function

Question

I'm reading a library file timer.h for STM core library that I just installed in Arduino hardware folder.

Of course, there has to be a lot of questions for me as a beginner about many approaches/stratgegies that programmers rule in writing the code.

One thing is that calling a function with a function pointer that only call one function, but the difference is that the function pointer is declared/defined as an inline function.

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Edit: I deleted the code and posted a link for it in github.

stm32/timer header file

OK, the part that I started to think about starts from line 595.

It's functions declarations.

In line 598, it's a declaration for a function that receiver a pointer to a function.

In later lines, starting from line 634, these functions have only one line to execute. So my question is why to develop a function to only execute one line ?

Why they didn't just put that line directly instead of putting it inside function ?

• Edgar Bonet: Could you please post a link to the complete file?
• chrisl: Where exactly is the function pointer here, that is called? bb_perip is not a function pointer, I think, but a function, that returns a pointer to a variable. Though I cannot be sure from this snippet of code alone
• R1S8K: ...\Program_Files\Arduino\hardware\Arduino_STM32-master\STM32F1\system\libmaple\include\libmaple for example depending on the root file location on my computer.
• R1S8K: I posted like most the inline functions. Couldn't post the complete code that is far more that the character limitations over 30000 character.
• chrisl: Again I don't see a function pointer being used here. Please point us, where exactly you are seeing the problem. Also can you please give a link to your used STM32 core, so that we can read this file on the web. I personally don't have a STM32-core installed, also we don't know, which core you used. Best case would be a github link to the file in question.

Answer 1

bb_perip is a function that returns a pointer to a bit from a register that is related to a specific timer peripheral (there's more than one). That pointer is then dereferenced with the * operator to make *bb_perip(...).

What bb_perip returns is dependent on what timer you are using and what value you are interested in.

bb_perip is not a pointer to a function, it is a normal function that happens to return a pointer.

• R1S8K: Something new to me is that there is an integer passed to this function ! It's my first time to encounter this feature. *bb_perip(&(dev->regs).bas->CR1, TIMER_CR1_CEN_BIT) = 0; there is a 0 passed to this function, how this is done ?
• Majenko: No, the integer is not being passed to the function. The integer is being assigned to the dereferenced pointer returned from the function.
• R1S8K: oooh I'm sorry my mistake I wanted to say "assigned" not "passed" :) totally different approaches. Yeah, I meant it's a new feature to me to assign anything to a function.
• R1S8K: Or because it's a function pointer, where the pointer is a variable basically, so I can assign a value for it. is that correct ?
• Majenko: You are not assigning anything to the function. The function returns a pointer to somewhere in memory. You take that pointer, then use it to place a value into memory at that address. Once the function has returned the pointer it has no further role to play. You can just as well use (in pseudocode) *func() = 4 as you can pointer = func(); *pointer = 4; - all you're doing is leaving out the middleman.