在preprocessor取下不断投 [英] Remove cast from constant in preprocessor

问题描述

在一个微控制器code，我利用那里有许多定义常量生产者提供一个图书馆。我想如果有我的一些常数之间的不匹配（与微控制器外组件共享，以 git的子树）和微控制器常量给一个错误。

In a microcontroller code, I am using a library provided by the producer where there are many constants defined. I'm trying to give an error if there's a mismatch between some of my constants (shared with components outside the microcontroller, with git-subtree) and the microcontroller constants.

例如，该库定义：

#ifdef SOME_PARTICULAR_MODEL
#define FLASH_BLOCK_SIZE ((uint8_t)64)
/* else, other models */
#endif

和地方，在微控制器code和在PC上整理了一些code之间共享的头，我有，例如：

And somewhere, in a header shared between the microcontroller code and some code compiled on the PC, I have for example:

#define MYPROG_BLOCK_SIZE 64

，并确保这些常量匹配，在微控制器code，其中两个常量存在，我有：

And to make sure these constants match, in the microcontroller code, where both constants exist, I have:

#if MYPROG_BLOCK_SIZE != FLASH_BLOCK_SIZE
#error "mismatch between actual block size and defined block size"
#endif

这是为了确保如果code是不断移植到一个更大的微控制器，共享的头也将被更新。

This is to make sure if the code is ever ported to a bigger microcontroller, the shared header would also be updated.

的问题是，这被简化为：

The problem is that this gets reduced to:

#if 64 != ((uint8_t)64)

这我不知道，如果是有效的 C ，但仍然让编译器呛。测试中，我发现，这个问题是不是 uint8_t有是一个typedef，它仍然带有强制转换为 INT 例如

which I'm not sure if is valid C, but nonetheless makes the compiler choke up. Testing, I found out that the problem is not that uint8_t is a typedef and it still chokes up with a cast to int for example.

有没有一种方法，从定义为（（uint8_t有）64）（uint8_t有）部分>？如果没有，有没有办法让前pression变成一个没有一个投去改变它？

Is there a way to remove the (uint8_t) part from a value defined as ((uint8_t)64)? If not, is there any way to change it so the expression turns into one without a cast?

我想过定义 uint8_t有的东西和＃如果，但我想不出后取消定义它出如何避免的投性质（Y）X 键，把它变成一个算术前pression。

I thought about defining uint8_t as something and undefining it after the #if, but I can't figure out how I can avoid the cast nature of (Y)X and turn it into an arithmetic expression.

推荐答案

下面是一个改进版本（第一个版本是下文）。这其中不依赖于投是 uint8_t有;它将与形式的任何 FLASH_BLOCK_SIZE 更换工作列表（（某些类型的）数）。

Here is an improved version (the first version is below). This one does not depend on the cast being uint8_t; it will work with any FLASH_BLOCK_SIZE replacement list of the form ((some type) number).

#define MYPROG_BLOCK_SIZE   64
#define FLASH_BLOCK_SIZE    ((uint8_t)64)

#define B(x)
#define C(x)    B x
#define D(x)    C x

#if MYPROG_BLOCK_SIZE != D(FLASH_BLOCK_SIZE)
    #error "mismatch between actual block size and defined block size"
#endif

下面是原始版本：

#define MYPROG_BLOCK_SIZE  64
#define FLASH_BLOCK_SIZE   ((uint8_t)64)

#define uint8_t             
#define Helper(x)          x
#define Deparenthesize(x)  Helper x

#if MYPROG_BLOCK_SIZE != Deparenthesize(Deparenthesize(FLASH_BLOCK_SIZE))
    #error "mismatch between actual block size and defined block size"
#endif
#undef uint8_t

在写code，我会preFER一个静态断言，但上面做什么，你在preprocessor要求。

When writing code, I would prefer a static assert, but the above does what you requested in the preprocessor.

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