Printf width specifier to maintain precision of floating-point value

Question

Is there a printf width specifier which can be applied to a floating point specifier that would automatically format the output to the necessary number of s

Answer 1

To my knowledge, there is a well diffused algorithm allowing to output to the necessary number of significant digits such that when scanning the string back in, the original floating point value is acquired in dtoa.c written by Daniel Gay, which is available here on Netlib (see also the associated paper). This code is used e.g. in Python, MySQL, Scilab, and many others.