如何检查宏中的常量值 [英] Howto check value of constants in a macro
问题描述
我想定义几个常量并确保它们都比给定的其他常量小
。我认为这可以通过
简单宏来完成。这样的事情：
#define MAX 999
#define DEF_CHECKED_VAL（名称，值）#if（值< MAX）\
#define name MAX \
#else \
#define name value \
#endif
所以
DEF_CHECKED_VAL（test_1,33）应扩展为#define test_1 33
和
DEF_CHECKED_VAL（test_2,1000）应该产生#define test_2 999
你可能知道（我今天学到的）这不起作用。对于这个问题最常见的
相关的常见问题解答似乎是10.25我有这个棘手的
预处理我想做什么而且我不能想出一个这样做的方法。
不幸的是，编写我自己的预处理器并不是一个真正的选择，而且我不能相信我是第一个谁想要实现这个
功能。我的问题是否有一个众所周知的解决方案，或者我在做什么
从根本上说是愚蠢的东西？
感谢您的帮助，Rick
Hi,
I''d like to define several constants and make sure that all of them are
smaller than a given other constant. I thought this could be done by a
simple macro. Something like this:
#define MAX 999
#define DEF_CHECKED_VAL( name, value) #if (value < MAX) \
#define name MAX \
#else \
#define name value \
#endif
So
DEF_CHECKED_VAL(test_1, 33) should expand to #define test_1 33
and
DEF_CHECKED_VAL(test_2, 1000) should yield #define test_2 999
As you probably know (and I learned today) this doesn''t work. The most
relevant FAQ to this problems seems to be "10.25 I''ve got this tricky
preprocessing I want to do and I can''t figure out a way to do it."
Unfortunately writing my own preprocessor isn''t really an option and I
can''t believe that I''m the first one who''d like to implement this
functionality. Is there a well-known solution to my problem, or am I doing
something fundamentally stupid?
Thanks for any help, Rick
推荐答案
Richard Meister< r。******* @ t-online.de>写道：
Richard Meister <r.*******@t-online.de> writes:
我想定义几个常量，并确保它们都比给定的其他常量小。我认为这可以通过一个简单的宏来完成。这样的事情：
#define MAX 999
#define DEF_CHECKED_VAL（名称，值）#if（值< MAX）\
#define name MAX \\＃
#else \
#define名称值\
#endif
所以
DEF_CHECKED_VAL（test_1,33）应扩展为#define test_1 33
和DEF_CHECKED_VAL（test_2,1000）应该产生#define test_2 999
I''d like to define several constants and make sure that all of them are
smaller than a given other constant. I thought this could be done by a
simple macro. Something like this:
#define MAX 999
#define DEF_CHECKED_VAL( name, value) #if (value < MAX) \
#define name MAX \
#else \
#define name value \
#endif
So
DEF_CHECKED_VAL(test_1, 33) should expand to #define test_1 33
and
DEF_CHECKED_VAL(test_2, 1000) should yield #define test_2 999
我认为上面的#if逻辑与你的例子相反，以便
<应该是> ;.
这是一个可能的解决方案：
#define DEF_CHECKED_VAL（名称，值）\
enum {name =（value）< MAX？ （值）：MAX};
-
int main（void）{char p [] =" ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz。\
\ n"，* q =" kl BIcNBFr.NKEzjwCIxNJC" ;; int i = sizeof p / 2; char * strchr（）; int putchar（\
）; while（* q ）{i + = strchr（p，* q ++） - p; if（i> =（int）sizeof p）i- = sizeof p-1; putchar（p [i] \
） ;}返回0;}
I think the #if logic above is opposite your examples, so that
the < should be >.
Here is one possible solution:
#define DEF_CHECKED_VAL(name, value) \
enum { name = (value) < MAX ? (value) : MAX };
--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}
Ben Pfaff< bl*@cs.stanford.edu>写道：
Ben Pfaff <bl*@cs.stanford.edu> writes:
Richard Meister< r。******* @ t-online.de>写道：
Richard Meister <r.*******@t-online.de> writes:
我想定义几个常量，并确保它们都比给定的其他常量小。我认为这可以通过一个简单的宏来完成。这样的事情：
#define MAX 999
#define DEF_CHECKED_VAL（名称，值）#if（值< MAX）\
#define name MAX \\＃
#else \
#define名称值\
#endif
所以
DEF_CHECKED_VAL（test_1,33）应扩展为#define test_1 33
和DEF_CHECKED_VAL（test_2,1000）应该产生#define test_2 999
I''d like to define several constants and make sure that all of them are
smaller than a given other constant. I thought this could be done by a
simple macro. Something like this:
#define MAX 999
#define DEF_CHECKED_VAL( name, value) #if (value < MAX) \
#define name MAX \
#else \
#define name value \
#endif
So
DEF_CHECKED_VAL(test_1, 33) should expand to #define test_1 33
and
DEF_CHECKED_VAL(test_2, 1000) should yield #define test_2 999
我认为上面的#if逻辑与你的例子相反，所以< <<应该是> ;.
这是一个可能的解决方案：
#define DEF_CHECKED_VAL（名称，值）\
枚举{name =（value）< MAX？ （值）：MAX};
I think the #if logic above is opposite your examples, so that
the < should be >.
Here is one possible solution:
#define DEF_CHECKED_VAL(name, value) \
enum { name = (value) < MAX ? (value) : MAX };
哦，这很聪明！
如果你需要更复杂的东西，不能用
整数值和常量表达式表示，你总是可以实现你的* b $ b自己的* simple *预处理器。没有必要编写一个完全的
功能的C预处理器，只需要一个产生C代码的程序作为其
输出。
例如，给定这样的输入：
MAX 999
DEF_CHECKED_VAL test_1 33
DEF_CHECKED_VAL test_2 1000
程序可以产生以下输出：
#define test_1 33
#define test_2 999
在构建过程中，您可以运行程序并生成一个
头文件，然后由C源文件包含#included。定义
您喜欢的转换语法和语义;
越简单，就越容易实现。
（就我个人而言，我会使用Perl这样的东西，但它可以
当然可以在C中完成。）
-
Keith Thompson（The_Other_Keith） ks *** @ mib.org < http://www.ghoti.net/~kst>
圣地亚哥超级计算机中心< * GT; < http://users.sdsc.edu/~kst>
我们必须做点什么。这是事情。因此，我们必须这样做。
Oooh, that''s clever!
If you need something more complex, that can''t be expressed with
integer values and constant expressions, you can always implement your
own *simple* preprocessor. There''s no need to write a fully
functional C preprocessor, just a program that produces C code as its
output.
For example, given an input like this:
MAX 999
DEF_CHECKED_VAL test_1 33
DEF_CHECKED_VAL test_2 1000
the program could produce the following output:
#define test_1 33
#define test_2 999
In your build procedure, you can run your program and generate a
header file that''s then #included by your C source files. Define
whatever syntax and semantics you like for the tranformation; the
simpler it is, the easier it will be to implement.
(Personally, I''d use Perl for something like this, but it can
certainly be done in C.)
--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
Richard Meister写道：
Richard Meister wrote:
我'我想定义几个常数，并确保它们都比给定的其他常数小。我认为这可以通过一个简单的宏来完成。
Hi,
I''d like to define several constants and
make sure that all of them are
smaller than a given other constant. I thought this could be done by a
simple macro.
我使用断言宏。
#include< assert.h>
void assert（标量表达式）;
-
皮特
I use the assert macro for that.
#include <assert.h>
void assert(scalar expression);
--
pete
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