Embedding macro values in strings

[Paul John Falstad]

In article <1991Jan10.200806.12745 at grep.co.uk> frank at grep.co.uk (Frank Wales) writes:
>For example, suppose I have  foo(__LINE__); in my source, and I want that
>to expand to  bar("Line n"); where n is substituted with the actual value
>of __LINE__ at that point.  Trying
>
>  #define foo(n)	bar("Line "#n)
>
>and invoking as  foo(10); yields  bar("Line 10"); , whereas  foo(__LINE__);
>yields  bar("Line __LINE__"); .

You realize, of course, that foo(10) would not actually produce:

   bar("line 10"),

but will produce:

	bar("line " "10")

wish is concatenated into a single string in a later phase of
compilation.  Just clarifying that.

Anyway, adding another level of macro expansion does the trick:

#define foo(n) bar("Line "fee(n))
#define fee(X) #X
foo(10)
foo(__LINE__)

This produces the intended result (using gcc):

bar("Line ""10" ) 
bar("Line ""4" ) 

--
Paul Falstad, pfalstad at phoenix.princeton.edu PLink:HYPNOS GEnie:P.FALSTAD
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