Question

my understanding is that most implementations of printf rely on something like

vsnprintf( _acBuffer[0], sizeof( _acBuffer[0] ), pcFormat, *ptArgList );

to actually handle the formatting and then they output them to the stream via puts.

Are there any implementation that minimize the size of _acBuffer[0] required while maintaining the ability to print all string?

Obviously something like :

printf("%s", pcReallyLongString);

would be a problem.

Your thoughts are much appreciated!

Answer 1

Your understanding is just wrong. I’ve never seen or heard of a printf implementation that works by first formatting the entire output to a temporary string buffer. Usually printf is done the other way around: the fundamental building block is vfprintf and vsnprintf is a wrapper for that which creates a fake FILE whose buffer is the destination string.

Edit: Some popular (e.g. glibc) implementations do make some use of unboundedly-large intermediate buffers for certain formats, especially wide character conversions, and will fail unpredictably when they cannot allocate sufficient memory for the buffer. This is purely a low-quality-implementation issue, however; there’s no fundamental reason any of the printf functions should require any more than a small constant amount of working space, regardless of what they’re printing.