在宏函数中使用数值常量
我正在为我的 AVR 编写一个简单的库，我想尝试使用宏函数来定义我的波特率。 AVR库中的很多函数以及我想写的宏都使用了F_CPU宏。
这是我对宏定义和我假设的实现的内容：
#define BAUD_SELECT(baud) ((F_CPU)/(2*baud)-1)
myubrr = BAUD_SELECT(38400);
我尝试使用 #define F_CPU 8000000UL，也在 make 文件中使用 -D"F_CPU 8000000UL" 但我总是在实现行遇到相同的错误。
expected ')' before numeric constant
我确信这与我滥用 #define 有关，宏定义位于头文件中，实现位于相应的 .c 文件中，F_CPU 定义位于 makefile 或另一个 main.c 文件中。
编辑 我按照建议更改了括号并运行了预处理器并找到了输出文件（至少我认为）
unsigned int myubrr = ((8000000UL 1)/(2*(baud))-1);
它在 F_CPU 应该在的位置放置了一个额外的 1，我对预处理器没有经验，所以我不知道如何使它不这样做，但也许这就是问题所在？
I'm writing a simple library for my AVR, and I wanted to try to use a macro function to define my baud-rate. A lot of the functions in the AVR's library use the macro F_CPU as well as the one I want to write.
Here's what I have for the macro definition and my supposed implementation:
#define BAUD_SELECT(baud) ((F_CPU)/(2*baud)-1)
myubrr = BAUD_SELECT(38400);
I have tried using #define F_CPU 8000000UL, and also in the make file as -D"F_CPU 8000000UL" but I always get the same error at the implementation line.
expected ')' before numeric constant
I'm sure it has something to do with my abuse of #define, and that the macro definition is in a header file, the implementation in the appropriate .c file, and the F_CPU definition either in the makefile or another main.c file.
EDIT
I made the parenthesis change as suggested and ran the preprocessor and found the output file (atleast I think)
unsigned int myubrr = ((8000000UL 1)/(2*(baud))-1);
It places an extra 1 where F_CPU should be, I'm not experienced with the preprocessor so I'm not sure how to make it not do that, but perhaps that is the problem?
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尝试将其括在括号中：
Try wrapping it in parentheses:
这对我来说效果很好：
当我使用
额外的括号进行编译时，在这种特定情况下并不重要，一般认为它们是一个好主意。所以还有其他事情发生。也许在其他头文件中还有另一个
F_CPU定义，它会覆盖您对F_CPU的定义This works fine for me:
when I compile with
The extra parens don't really matter in this specific case, thought they're a good idea in general. So there's something else going on. Perhaps there's another definition of
F_CPUin some other header file that is overriding your definition ofF_CPU