宏重新定义 [英] Macro redefinition
问题描述
我正在实现一个解析器，其中定义了很多不同的数据
元素。现在不是手工编码X定义，而是表初始化所需的大量行数，我决定生成
这个来源。
所以，我基本上使用了这个技巧：
void gen_source_function（FILE * out）
{
#define EXPAND_DEF（ NUM，名称）generate_source_1（下，NUM，＃NAME）
的#include" iso8583_defs"
的#define EXPAND_DEF（NUM，名称）generate_source_2（下，num，＃name）
#include" iso8583_defs"
}
其中iso8583_defs ;确实包含了很多这样的行：
EXPAND_DEF（1，FIELD_NAME）;
EXPAND_DEF（2，ANOTHER_FIELD_NAME）;
我的问题很简单，上面的C代码是否允许？
-
Tor< torust [at] online [dot] no>
I''m implementing a parser, where there is a lot of different data
elements defined. Now instead of hand-coding X defines, and the massive
number of lines needed for table initialization, I decided to generate
this source instead.
So, I basically used this trick:
void gen_source_function(FILE *out)
{
#define EXPAND_DEF(num, name) generate_source_1(out, num, #name)
#include "iso8583_defs"
#define EXPAND_DEF(num, name) generate_source_2(out, num, #name)
#include "iso8583_defs"
}
where the "iso8583_defs" file, did contain a lot of lines like this:
EXPAND_DEF(1, FIELD_NAME);
EXPAND_DEF(2, ANOTHER_FIELD_NAME);
My question is simply, is the above C code allowed?
--
Tor <torust [at] online [dot] no>
推荐答案
Tor Rustad< to ******** @ hotmail.comwrites：
Tor Rustad <to********@hotmail.comwrites:
void gen_source_function（FILE * out）
{
#define EXPAND_DEF（num，name）generate_source_1（out，num，＃name）
的#include" iso8583_defs"
的#define EXPAND_DEF（NUM，名称）generate_source_2（下，NUM，＃NAME）
的#include" iso8583_defs" < br $>
}
其中iso8583_defs确实包含了很多这样的行：
EXPAND_DEF（1，FIELD_NAME）;
EXPAND_DEF（2，ANOTHER_FIELD_NAME）;
我的问题很简单，是否允许上述C代码？
void gen_source_function(FILE *out)
{
#define EXPAND_DEF(num, name) generate_source_1(out, num, #name)
#include "iso8583_defs"
#define EXPAND_DEF(num, name) generate_source_2(out, num, #name)
#include "iso8583_defs"
}
where the "iso8583_defs" file, did contain a lot of lines like this:
EXPAND_DEF(1, FIELD_NAME);
EXPAND_DEF(2, ANOTHER_FIELD_NAME);
My question is simply, is the above C code allowed?
当然。很多代码都使用这个技巧来避免冗余。
如果你不喜欢使用包含文件的想法，那你
也可以使用宏：
void gen_source_function（FILE * out）
{
#define ISO8583_DEFS \
EXPAND_DEF（1，FIELD_NAME）; \
EXPAND_DEF（2，ANOTHER_FIELD_NAME）;
#define EXPAND_DEF（num，name）generate_source_1（out，num，＃name）
ISO8583_DEFS
#define EXPAND_DEF（num，name）generate_source_2（out，num，＃name）
ISO8583_DEFS
}
我认为这是一个更好的折腾。两者都不漂亮，
都有效。
-
char a [] =" \ n .CJacehknorstu" ;; int putchar （INT）; INT主（无效）{无符号长b []
= {0x67dffdff，0x9aa9aa6a，0xa77ffda9,0x7da6aa6a，0xa6 7f6aaa，0xaa9aa9f6,0x11f6}，* p
= b，i = 24; for（; p + =！* p; * p / = 4）switch（0 [p]& 3）case 0：{return 0; for（p - ; i--; i - ）case +
2：{i ++; if（i）break; else default：continue; if（0）case 1：putchar（a [i& 15]）; break;}} }
Sure. Lots of code uses this trick to avoid redundancy.
If you don''t like the idea of using an include file for this, you
can also use a macro:
void gen_source_function(FILE *out)
{
#define ISO8583_DEFS \
EXPAND_DEF(1, FIELD_NAME); \
EXPAND_DEF(2, ANOTHER_FIELD_NAME);
#define EXPAND_DEF(num, name) generate_source_1(out, num, #name)
ISO8583_DEFS
#define EXPAND_DEF(num, name) generate_source_2(out, num, #name)
ISO8583_DEFS
}
I think it''s a toss-up which is better. Neither is pretty, both
are functional.
--
char a[]="\n .CJacehknorstu";int putchar(int);int main(void){unsigned long b[]
={0x67dffdff,0x9aa9aa6a,0xa77ffda9,0x7da6aa6a,0xa6 7f6aaa,0xaa9aa9f6,0x11f6},*p
=b,i=24;for(;p+=!*p;*p/=4)switch(0[p]&3)case 0:{return 0;for(p--;i--;i--)case+
2:{i++;if(i)break;else default:continue;if(0)case 1:putchar(a[i&15]);break;}}}
8月31日上午11点04分，Tor Rustad< tor_rus ... @ hotmail.comwrote：
On Aug 31, 11:04 am, Tor Rustad <tor_rus...@hotmail.comwrote:
我正在实现一个解析器，其中定义了很多不同的数据
元素。现在不是手工编码X定义，而是表初始化所需的大量行数，我决定生成
这个来源。
所以，我基本上使用了这个技巧：
void gen_source_function（FILE * out）
{
的#define EXPAND_DEF（NUM，名称）generate_source_1（下，NUM，＃NAME）
的#include" iso8583_defs"
的#define EXPAND_DEF（NUM，名称）generate_source_2（out，num，＃name）
#include" iso8583_defs"
}
where iso8583_defs确实包含了很多这样的行：
EXPAND_DEF（1，FIELD_NAME）;
EXPAND_DEF（2，ANOTHER_FIELD_NAME）;
我的问题很简单，上面的C代码是允许的吗？
I''m implementing a parser, where there is a lot of different data
elements defined. Now instead of hand-coding X defines, and the massive
number of lines needed for table initialization, I decided to generate
this source instead.
So, I basically used this trick:
void gen_source_function(FILE *out)
{
#define EXPAND_DEF(num, name) generate_source_1(out, num, #name)
#include "iso8583_defs"
#define EXPAND_DEF(num, name) generate_source_2(out, num, #name)
#include "iso8583_defs"
}
where the "iso8583_defs" file, did contain a lot of lines like this:
EXPAND_DEF(1, FIELD_NAME);
EXPAND_DEF(2, ANOTHER_FIELD_NAME);
My question is simply, is the above C code allowed?
这是我工作的代码中非常常见的习语。一个警告：不要在重新定义之前忘记#undef EXPAND_DEF。
问候，
- = Dave
It''s a pretty common idiom in the code I work with. One caveat: don''t
forget to #undef EXPAND_DEF before redefining it.
Regards,
-=Dave
Ben Pfaff写道：
Ben Pfaff wrote:
Tor Rustad< to *** *****@hotmail.comwrites：
Tor Rustad <to********@hotmail.comwrites:
> void gen_source_function（FILE * out）
{
#define EXPAND_DEF（num， name）generate_source_1（out，num，＃name）
#include" iso8583_defs"
#define EXPAND_DEF（num，name）generate_source_2（out，num，＃name）
#include" iso8583_defs"
其中iso8583_defs文件，确实包含很多这样的行：
EXPAND_DEF（1，FIELD_NAME）;
EXPAND_DEF（2，ANOTHER_FIELD_NAME）;
我的问题很简单，允许上面的C代码？
>void gen_source_function(FILE *out)
{
#define EXPAND_DEF(num, name) generate_source_1(out, num, #name)
#include "iso8583_defs"
#define EXPAND_DEF(num, name) generate_source_2(out, num, #name)
#include "iso8583_defs"
}
where the "iso8583_defs" file, did contain a lot of lines like this:
EXPAND_DEF(1, FIELD_NAME);
EXPAND_DEF(2, ANOTHER_FIELD_NAME);
My question is simply, is the above C code allowed?
当然。许多代码使用此技巧来避免冗余。
Sure. Lots of code uses this trick to avoid redundancy.
是的，这就是主意。
Yup, that''s the idea.
如果你不喜欢这个主意为此使用包含文件，你
也可以使用宏：
void gen_source_function（FILE * out）
{
#define ISO8583_DEFS \
EXPAND_DEF（1，FIELD_NAME）; \
EXPAND_DEF（2，ANOTHER_FIELD_NAME）;
#define EXPAND_DEF（num，name）generate_source_1（out，num，＃name）
ISO8583_DEFS
#define EXPAND_DEF（num，name）generate_source_2（out，num，＃name）
ISO8583_DEFS
}
If you don''t like the idea of using an include file for this, you
can also use a macro:
void gen_source_function(FILE *out)
{
#define ISO8583_DEFS \
EXPAND_DEF(1, FIELD_NAME); \
EXPAND_DEF(2, ANOTHER_FIELD_NAME);
#define EXPAND_DEF(num, name) generate_source_1(out, num, #name)
ISO8583_DEFS
#define EXPAND_DEF(num, name) generate_source_2(out, num, #name)
ISO8583_DEFS
}
有趣的是，我之前没有见过这个解决方案。
但是，有一个翻译限制逻辑
源代码行中的509个字符，并且在拼接之后不是逻辑源代码行
您的ISO8583_DEFS在上面？
-
Tor< torust [at] online [dot] no>
Interesting, I haven''t seen this solution before.
However, there is a translation limit of "509 characters in a logical
source line", and isn''t logical source lines made up after line-splicing
your ISO8583_DEFS above?
--
Tor <torust [at] online [dot] no>
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