5.10 Hex Floats
ISO C99 supports floating-point numbers written not only in the usual decimal notation, such as 1.55e1
, but also numbers such as 0x1.fp3
written in hexadecimal format. As a GNU extension, GCC supports this in C89 mode (except in some cases when strictly conforming) and in C++. In that format the `
0x
' hex introducer and the `
p
' or `
P
' exponent field are mandatory. The exponent is a decimal number that indicates the power of 2 by which the significant part will be multiplied. Thus `
0x1.f
' is 1 15/16, `
p3
' multiplies it by 8, and the value of 0x1.fp3
is the same as 1.55e1
.
Unlike for floating-point numbers in the decimal notation the exponent is always required in the hexadecimal notation. Otherwise the compiler would not be able to resolve the ambiguity of, e.g., 0x1.f
. This could mean 1.0f
or 1.9375
since `
f
' is also the extension for floating-point constants of type float
.