error: expected ';', ',' or ')' before numeric constant in Serial communication ATmega32

Question

I am trying to connect a Bluetooth module through serial communication. But the error which is " error: expected ';', ',' or ')' before numeric constant" occurred on the line where I defined the baud rate. can not find where the error is. Help would be appreciated, thanks!

#define BAUD_RATE 9600
#define BAUD_PreS (((F_CPU / (BAUD_RATE * 16UL))) - 1)

void USART_init(long BAUD_RATE){

       UCSRB |= (1 << RXEN ) | (1 << TXEN ) ;                   
       UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1) ;
       UBRRH  = (BAUD_PreS >> 8);
       UBRRL  = BAUD_PreS;
}

You can't use `BAUD_RATE` as a function argument, since it's a macro that expands into a number. You've written the equivalent of `void USART_init(long 9600)` — Barmar, Sep 15 '22 at 20:28
With the defines shown this line `void USART_init(long BAUD_RATE)` becomes `void USART_init(long 9600)` after preprocessing. You should choose a different name for the argument or remove it completely since you are not using it. — Retired Ninja, Sep 15 '22 at 20:28
`BAUD_RATE` shouldn't be a macro if you want to use it as the function parameter. — Barmar, Sep 15 '22 at 20:30

Ted Lyngmo · Answer 1 · 2022-09-15T20:32:06.153

1

The precompiler will replace BAUD_RATE with 9600, so this:

#define BAUD_RATE 9600
void USART_init(long BAUD_RATE){

becomes

#define BAUD_RATE 9600
void USART_init(long 9600){
//              ^^^^^^^^^

So, you need to give the variable in USART_init a different name - but, since it's not even used in the function, just remove it:

void USART_init(){

edited Sep 15 '22 at 20:32

answered Sep 15 '22 at 20:28

Ted Lyngmo

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Actually I think he needs to get rid of the macro, so `BAUD_PreS` will use the function parameter as intended. – Barmar Sep 15 '22 at 20:31
@Barmar Indeed. I added a comment – Ted Lyngmo Sep 15 '22 at 20:32
No, that's not what I meant. They need to get rid of `#define BAUD_RATE 9600` – Barmar Sep 15 '22 at 20:32
@Barmar `BAUD_PreS` is defined using `BAUD_RATE` – Ted Lyngmo Sep 15 '22 at 20:33
No it isn't. Remember, it's just a macro, it expands into an expression that uses that variable. – Barmar Sep 15 '22 at 20:34
@Barmar Sure, but you could either take it as a parameter as you suggest, or let it be a macro. `BAUD_PreS` will use `9600` after expansion. – Ted Lyngmo Sep 15 '22 at 20:39
I assume that the function is supposed to initialize to the requested baud rate, not a hard-coded default. – Barmar Sep 15 '22 at 20:40
@Barmar Could be. It'd certainly make it more flexible, but if someone writes `#define BAUD_RATE 9600` I expect that hardcoding to be deliberate - then again, the function signature suggests that it should be a runtime choice. Hard to guess. – Ted Lyngmo Sep 15 '22 at 20:41
I also think `USART_init(long BAUD_RATE)` is deliberate. One of them is wrong. – Barmar Sep 15 '22 at 20:43
@Barmar Absolute agreement. – Ted Lyngmo Sep 15 '22 at 20:43

score 1 · Answer 2 · answered Sep 15 '22 at 20:36

Get rid of the line

#define BAUD_RATE 9600

It looks like you want BAUD_PreS to expand into something that depends on the argument to USART_init(). So you shouldn't define that as a macro, it needs to get the value that was passed as the argument to the function.

Usually this type of macro is written as a function-style macro.

#define BAUD_PreS(r) (((F_CPU / ((r) * 16UL))) - 1)

Then you would use it as:

       UBRRH  = (BAUD_PreS(BAUD_RATE) >> 8);
       UBRRL  = BAUD_PreS(BAUD_RATE);

Yes, I think this is the better choice if the baud rate isn't supposed to be hardcoded to `9600`. — Ted Lyngmo, Sep 15 '22 at 20:44

error: expected ';', ',' or ')' before numeric constant in Serial communication ATmega32

2 Answers2