C Macro Filter String literals in arguments

[ruzip]

Is it possible to do a parse or filter in C a macro for example:

FILTER(Var, "text", somevar, foo, "moretext")

Becomes or expands to:

FILTER(Var, somevar, foo )


Old question:

INPUT(sometext <name1> sometext somemoretext <name2> moretext here)

and expands to a macro statement:

FILTER(<name1><name2>)

it just parse and retains the text enclosed in <> and ignores the rest.

[helios]

No, macros can't do text processing like that.

[ruzip]

Ok well how about ignore args that are
string literals in quotes?

So

FILTER(Var, "text", somevar, foo, "moretext")

Becomes or expands to:

FILTER(Var, somevar, foo )

I have updated my topic to reflect my use case
Since the old one is not possible.

[AbstractionAnon]

Again no.

You can change an argument to a quoted literal, but you can't go the other way.
Macros don't provide any way to test if an argument is a quoted literal.

[mbozzi]

Why not
#define IGNORE(...)
Then
WHATEVER_YOU_WANT(a, b, IGNORE(c), d)

[ruzip]

Thanks, but what i'm after is to first check whether the arg is a string literal.

[helios]

Can't be done, I'm afraid. You could look into passing the source through M4 before compiling. The M4 syntax is similar to the C preprocessor's.
https://www.gnu.org/software/m4/manual/m4.html
If you're going that route, though, you're probably better off just writing a small program that generates your source. Maintaining M4 input sucks.

[mbozzi]

The problem is that string literals are typically treated as being self-delimiting. This means that the normal pattern matching hack used to identify particular tokens can't work with double quotes.

Here's an example of the trick. Here the macro IS_DQUOTE expands to 1 if you pass in the word dquote but otherwise it expands to 0:

#define CONCATENATED0(a, ...) a##__VA_ARGS__
#define CONCATENATED(a, ...) CONCATENATED0(a, __VA_ARGS__)
#define SECOND(a, b, ...) b
#define IS_DQUOTE_PATTERN_dquote _, 1
#define IS_DQUOTE0(...) SECOND(__VA_ARGS__, 0)
#define IS_DQUOTE(a) IS_DQUOTE0(CONCATENATED(IS_DQUOTE_PATTERN_, a))

static_assert(IS_DQUOTE(dquote))
static_assert(IS_DQUOTE(anything else) == false)

https://coliru.stacked-crooked.com/a/404abcb9a144df9e

When trying to adapt this to identify actual quoted strings, the most immediate problem is that
CONCATENATED(IS_DQUOTE_PATTERN_, "")
is a syntax error.
This can be worked around by abusing UDL suffixes:
CONCATENATED("", _x_INVENTED_UDL_SUFFIX)()
But it still doesn't help because it appears that the resulting expansion, which is ""_x_INVENTED_UDL_SUFFIX(), won't expand even if _x_INVENTED_UDL_SUFFIX is a function-like macro.

Some alternatives might be:
WHATEVER_YOU_WANT(a, b, STRINGIFY(xyz), d)
or
WHATEVER_YOU_WANT(a, b, DQUOTE, c, DQUOTE, d)
or
WHATEVER_YOU_WANT(a, b, DQUOTE c DQUOTE, d)

Also, depending on what code is generated you might be able to use templates to do it.