printf with %a does not seem to produce a hexadecimal number

Question

I have been told that "%a" used in C's printf would display hexadecimal format of a number. To test it, I print out the representation of 2^10:

 printf ("%a", pow(2.0,10));

which gives

0x1p+10

I am confused because the exponent part "+10" looks more like a decimal format rather than a hexadecimal format. A hexadecimal format should have been 1pA . Where am I wrong?

Answer 1

It's correct, that format is called hexadecimal for double s.

The man page says:

For a conversion, the double argument is converted to hexadecimal notation (using the letters abcdef ) in the style [-]0xh.hhhp[+-]d [...] the exponent consists of a positive or negative sign followed by a decimal number representing an exponent of 2.

So it's correct that while the mantissa is in hex, the exponent is still decimal.