Or put differently, are there equivalents to intmax_t and %jd but for floating point numbers?
This has already been asked as a side question here, but the question is so large that I think people forgot to answer the side question. Also that was tagged as c++, and I'm looking for a c solution.
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To my knowledge C does not have extended floating point types. The only floating point types are float, double, and long double. Thus, %La, %Le, %Lf, %Lg, and long double seem to be your answers.
Some implementations may provide additional extended types, but they are completely outside the scope of the standard.
long long on any implementation (TODO please confirm this), but still I like the idea of using intmax_t just in case in 10 years a larger type becomes available.
intNN_t, etc. However, no similar provision is made for floating point, so extended floating point types could not be used as the definition for types like time_t or double_t in a conforming implementation.C11 does not have a floating point equivalents to intmax_t (Integer type with the maximum width supported.). Should C of the future define some sort of long long double, etc. the language presently has no seamless upgrade path to it.
C11 6.11.1.1 "Future standardization may include additional floating-point types, including those with greater range, precision, or both than long double." does point to the possibility of larger widths you envision.
The situation for floating-point numbers differs from integers in need. Various processors have had increasingly width integer widths over the years (8,16,32,64) and 128 on the horizon. Whereas gross floating-point size has been relatively more stable (4,8,10,16) , precision, range, encoding, rounding have taken up much FP concern. I suspect we'll see decimal and binary floating point specifications next.
Another difference is that integers grow in one dimension - range. FP can grow independently in range and precision, not to mention the peculiarities of base (2, 10, 16, etc.) Also see "IEEE 754" comment below.
Presently we have 3: C11 6.2.5.4 : float, double, and long double. Should you want to create a forward compatibly path you could prepare for a change with say typedef long double Xdouble, but then you may be obliged to write a lot of wrapper functions like Xdouble sinX(Xdouble x);, prepare many equivalent defines to DBL_MANT_DIG, PRIdN, etc. No small effort.
__int128_t and __uint128_t, for example.__int128 (but not __uint128), __uint128_t (but not __int128_t), and unsigned __int128. The documentation refers to __int128 and unsigned __int128. It's probably supported only on 64-bit targets.