Use macro for printing to stderr

[jeroen]

We use libxlswriter in R, but we are not supposed to use fprintf(stderr, ...) because applications and IDEs that embed the R interpreter ignore this. Instead the interpreter has a function REprintf(...) which packages call for text that the IDE or embedding application has to print to the user terminal.

So I would need some way to override the error-printing function, either at build time or at runtime. Here is a simple concept solution. This would allow me to compile libxlsxwriter with

CFLAGS += -DLXW_PRINT_ERR=REprintf

And thereby I get the desired behavior. Alternatively you could create some sort of set-callback, but that would be more involved.

The drawback of this approach I suppose is that variadic macros require c99, which is not a problem for me, but I don't know how else I would do this.

Thanks for you thoughts!

[jmcnamara]

The drawback of this approach I suppose is that variadic macros require c99, which is not a problem for me,

That, unfortunately, is a deal break for libxlsxwriter since it needs to maintain backward (in both senses of the word) compatibility with ANSI C for MS Visual C.

However, I think I can fix it so you can use REprintf. Let me work on a solution.

See also, #155, which is related.