Expand macros inside quoted string

c macros c-preprocessor c-strings
davide picture davide · Oct 18, 2012 · Viewed 40.3k times · Source

Possible Duplicate:
C Macros to create strings

I have a function which accepts one argument of type char*, like f("string");
If the string argument is defined by-the-fly in the function call, how can macros be expanded within the string body?

For example:

#define COLOR #00ff00
f("abc COLOR");

would be equivalent to

f("abc #00ff00");

but instead the expansion is not performed, and the function receives literally abc COLOR.

In particular, I need to expand the macro to exactly \"#00ff00\", so that this quoted token is concatenated with the rest of the string argument passed to f(), quotes included; that is, the preprocessor has to finish his job and welcome the compiler transforming the code from f("abc COLOR"); to f("abc \"#00ff00\"");

Answer

tomahh picture tomahh · Oct 18, 2012

You can't expand macros in strings, but you can write

#define COLOR "#00ff00"

f("abc "COLOR);

Remember that this concatenation is done by the C preprocessor, and is only a feature to concatenate plain strings, not variables or so.

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