Objective C - #define using __VA_ARGS__ - ios

Question

I am learning how to use macro but now confused with one.
I am trying to create a NSString concatenate which will just append every params to each other.
for example : concatOP(#"hey",#"Jude",#"Don't") would return a NSString containing : #"heyJudeDon't"
I actually made a bit of code (some found here as well) which get the number of params but I don't succeed to make the second part of the job.
#define NUMARGS(...) ( sizeof((int[]){__VA_ARGS__}) / sizeof(int) )
#define concatOP(...) NSMutableString *format = [[NSMutableString alloc] init];\
for( int i = 0; i < NUMARGS(__VA_ARGS__); i++){\
[format appendString:#"%#"];}\
[[NSString alloc] initWithFormat:format, __VA_ARGS__]
I actually get many errors, telling me that format doesn't exist or that I miss some ";" or other ending tags.

Answer 1

Here is yours macro:
#define concatOP(...) [#[__VA_ARGS__] componentsJoinedByString:#""]
EDIT:
if you unwind yours macro NSString* result = concatOP(#"hey",#"Jude",#"Don't");
you will get:
NSString* result = NSMutableString *format = [[NSMutableString alloc] init]; for( int i = 0; i < NUMARGS(#"hey",#"Jude",#"Don't"); i++){ format = [format appendString:#"%#"];} [[NSString alloc] initWithFormat:format, #"hey",#"Jude",#"Don't"];
Looks odd.

Answer 2

This doesn't exactly answer your question, but NSString literals are concatenated by the compiler, just like their C-counterparts, so this code works out of the box:
NSString *str = #"Hey" #"Jude" #"Don't";
which is the same as:
NSString *str = #"HeyJudeDon't";
This is typically used to split a long string literal across multiple lines of the source file.
Bottom line; you don't need all those messy macros and pointless methods to do this.

Answer 3

I don't know how to do this with macros.
You can do it in Objective C like:
Implement a method like:
- (NSString *)concateStrings:(NSString *)firstArg, ...
{
NSMutableString *concatString = [[NSMutableString alloc] init];
va_list args;
va_start(args, firstArg);
for (NSString *arg = firstArg; arg != nil; arg = va_arg(args, NSString*))
{
[concatString appendString:arg];
}
va_end(args);
return concatString;
}
You can call this method like:
NSLog(#"%#",[self concateStrings:#"hey",#"Jude",#"Don't",nil]) ;
Output:
heyJudeDon't
Make sure that you pass nil at the end.