Overwrite stdio functions

[akaeba]

Hi Charles,

the nanoprintf.h is a real great deal. Thanks for providing such an powerful tool. I have on addition in mind, to replace the stdio printf implementation by the npf_printf implementation. Enabling could be realized by compile switch. What do you think? I started a short google research:

• https://en.cppreference.com/w/cpp/preprocessor/replace
• http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html

Without testing it could look like follows:

#undef printf
#define printf(format, ...) npf_pprintf (format, ## __VA_ARGS__)

BR,
Andreas

[charlesnicholson]

Thanks for the kind words!

The C99 Standard defines printf (and friends) explicitly as a function- unfortunately #undef doesn't work on functions, only preprocessor symbols.

I guess there could be a compile-time flag into nanoprintf that renames functions, but I think there's still a problem:

Under the hood printf writes the content to the stdout io stream. printf(char const *fmt, ...) is generally implemented as fprintf(stdout, fmt, ...) for this reason; it's a shortcut. I could perhaps see it being helpful to have a compile-time build flag for nanoprintf that turns npf_snprintf into snprintf, and similarly turns npf_vsnprintf into vsnprintf. Though, if you simply write your own snprintf and vsnprintf wrappers that just return whatever the npf_ versions return, the compiler will optimize the shims out of existence.

Since nanoprintf is intended to replace stdio, though, I'd prefer that it not depend on stdio so that it can have access to the stdout symbol. Additionally, the per-byte output callback would have to write to the stdout stream, which means that nanoprintf would take a dependency on write.

My intent with nanoprintf was to be a building block for users who wanted to replace or re-implement printf, and to that end I think a big part of its power and flexibility come from its willful ignorance of write and stdout. To me it's one of those "less is more" scenarios :)

Anyway, I hope that was helpful!

[akaeba]

Hi Charles,
thanks for the explanaition. It looks much complexer then i thought at begin. Are all valid arguments. I'll try it in my embedded project to overwrite the function. Thanks :)

BR,
Andreas