Concat string with __VA_ARGS__

Question

I've the following macro:

 #define MY_FCT1( id, ... )       \
    FCT( id,__VA_ARGS__ );        \

and I want to create a new one to do something like this:

 #define MY_FCT2( id, ... )                           \
    MY_FCT1( id, (" %s : ",Name())" "__VA_ARGS__);    \

but I get the following error:

error: expression cannot be used as a function

Anyone have an idea how to solve this issue please?

I only see that your code is wrong. What is it supposed to do? — Matt, Mar 06 '15 at 10:06
it must add the returned string from Name() function to the given arguments of MY_FCT1 — Armageddon, Mar 06 '15 at 10:12
no doesn't work, I get this error: error: expected ')' before 'Name' — Armageddon, Mar 06 '15 at 12:55
I try this: MY_FCT1( id, " %s : "__VA_ARGS__, Name()); but I get Name() after __VA_ARGS__ — Armageddon, Mar 06 '15 at 13:11

luser droog · Answer 1 · 2015-03-14T18:32:02.957

It isn't clear exactly what you're trying to do. A macro cannot call a function. A macro can yield replacement text which includes a function call, but the function won't be called until runtime.

To add Name() to the __VA_ARGS__ which MY_FCT1 receives, just add it like a normal argument with a comma.

 #define MY_FCT2( id, ... )                           \
    MY_FCT1( id, Name(), __VA_ARGS__);

You appear to be trying to use a quoted space character as a concatenation operator. The operator for this (only valid in the replacement text of a macro) is ##. Eg.

#define CAT(x,y) x ## y
//or
#define CAT(x,y) x##y
//                ^ ^    spaces are not relevant here

Concat string with __VA_ARGS__

1 Answers1