Complicated multi-argument #define macro for strings

Question

I'm working on a project and have a problem that I believe can be solved with macros, but given the nature of the issue I don't have the experience to write one myself.

Here's what I would expect as input and output of the #define macro:

Inputting code such as this

printf(foobar(Hello World.));

Should result in the preprocessor producing code that reads:

printf((char *)(std::string("")+'H'+'e'+'l'+'l'+'o'+' '+'W'+'o'+'r'+'l'+'d'+'.').c_str());

I'm assuming something this complicated is possible, and I hope one of you guys can help me out.

I NEED IT TO BE A MACRO, I DO NOT want a string constant anywhere.

Answer 1

Uh, I fear it is impossible (unless I don't know something). I believe there is no macro to split a given input token (eg Hello) into characters building it (H ello)

There were some attempts to do such thing, but I fear it is not exactly what you need:

C++: Can a macro expand "abc" into 'a', 'b', 'c'?

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"More powerful precompiler" ?

Try this topic: Replacements for the C preprocessor

Answer 2

The only solution I can think of is to run your code through a suitable script (probably just some light awk ), that does the substitution before your code reaches the pre-compiler.

Depending on your environment you could do this as a "Pre-Build Event" in Visual Studio, or just add a step directly into your makefile.

Answer 3

Macros are basically substitution or addition of strings. You could do this with a pre-processor of your own, but the standard pre-processor won't split strings into component parts.

How about this: Put all these (assuming there is more than one) 'macros' in a separate file. Write a program that translates them into the expansion you require and then include THAT file in your c program? You could then make the expansion program part of your make file so it's always up to date. Using a separate file makes the expansion program much easier than parsing ac/c++ file.

Answer 4

Since you're looking for a narrow, direct answer to your question and without suggestions, here goes:

This is impossible. You must find a different solution to whatever it is you're trying to achieve.

Answer 5

Have you tried:

#define toString(x) #x

You can use it after like this:

printf("%s", toString(hello world));

Don't try to use printf directly with the string because you can have format specifier in the string.

printf(toString(hello world)); //wrong, you can have for example %d in the string