单引一个宏参数 [英] single-quoting a macro argument

问题描述

是否可以编写一个单引号参数的宏？


#define SOME_MACRO（x）


这样SOME_MACRO （foo）扩展为''foo''


谢谢，

Marius

Is it possible to write a macro that single-quotes its argument?

#define SOME_MACRO(x)

such that SOME_MACRO(foo) expands to ''foo''

Thanks,
Marius

推荐答案

" Marius Lazer" <毫安********** @ gmail.com>写道：

＃是否可以编写一个单引号参数的宏？

＃

#define SOME_MACRO（x）

＃

＃这样SOME_MACRO（foo）扩展为''foo''


对于单个角色你可以做

#define LITERAL（x）（*＃x）

也许编译器可以优化内存参考。


For多个角色，你或许可以逃脱一些像

#define LITERAL（x）（*（（int *）#x" \0\0\0\ 0 \\\\\\\ 0"））

但这是假设编译器如何存储字符串。


除非你需要做一个常数的特殊原因，

你可以做一些像

int literalise（char * s）{

int i，v; unsigned char * u =（unsigned char *）s;

for（i = 0，v = 0; u [i]&& i< sizeof v; i ++）

v =（v<< CHAR_BIT）|你[$]

返回v;

}

literalise（" foo"）;

这也是避免依赖于实现的解释

多字符文字，endianess和内存对齐

问题。


-

SM Ryan http://www.rawbw.com/~wyrmwif/

标题没有规定行为。

"Marius Lazer" <ma**********@gmail.com> wrote:
# Is it possible to write a macro that single-quotes its argument?
#
# #define SOME_MACRO(x)
#
# such that SOME_MACRO(foo) expands to ''foo''

For a single character you can do
#define LITERAL(x) (*#x)
and perhaps the compiler can optimise away the memory reference.

For multiple characters, you might be able to get away with some like
#define LITERAL(x) (*((int*)#x "\0\0\0\0\0\0\0\0"))
but that''s making assumptions about how the compiler stores strings.

Unless there''s particular reason you need to make a constant,
you can do something like
int literalise(char *s) {
int i,v; unsigned char *u = (unsigned char*)s;
for (i=0,v=0; u[i] && i<sizeof v; i++)
v = (v<<CHAR_BIT) | u[i]
return v;
}
literalise("foo");
which also avoids implementation dependent interpretation of
multi-character literals, endianess, and memory alignment
questions.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
Title does not dictate behaviour.

我的意思是扩展到''foo''，而不是它''第一个字符。

这里没有价值语义。


#define SOME_MACRO（x）#x


SOME_MACRO（foo）扩展为foo但是我需要''foo''


我尝试了类似这样的东西，但是不是我需要的东西：


#define QUOTE ''

#define SOME_MACRO（x）QUOTE x QUOTE


SOME_MACRO（foo）扩展为''foo''（用空格代替''foo' ''）。


谢谢，

Marius

I meant literally expansion to ''foo'', not to it''s first character.
There are no value semantics here.

#define SOME_MACRO(x) #x

SOME_MACRO(foo) expands to "foo" but I need ''foo''

I tried something like this which is close but not exactly what I need:

#define QUOTE ''
#define SOME_MACRO(x) QUOTE x QUOTE

SOME_MACRO(foo) expands to '' foo '' (with spaces instead of ''foo'').

Thanks,
Marius

" Marius Lazer" ; <毫安********** @ gmail.com>写道：

"Marius Lazer" <ma**********@gmail.com> writes:

我的意思是扩展到''foo''，而不是它的第一个字符。
这里没有价值语义。

#define SOME_MACRO（x）#x

SOME_MACRO（foo）扩展为foo但是我需要''foo''

I meant literally expansion to ''foo'', not to it''s first character.
There are no value semantics here.

#define SOME_MACRO(x) #x

SOME_MACRO(foo) expands to "foo" but I need ''foo''

我认为你不能从C预处理器中得到你想要的东西。

- -

我没有那个方便的C& V，但我有Dan Pop。

--E。 Gibbons

I don''t think you can get what you want from the C preprocessor.
--
"I don''t have C&V for that handy, but I''ve got Dan Pop."
--E. Gibbons

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