Question

I am doing some input/output between a c++ and a python program (only floating point values) python has a nice feature of converting floating point values to hex-numbers and back as you can see in this link:

http://docs.python.org/library/stdtypes.html#additional-methods-on-float

Is there an easy way in C++ to to something similar? and convert the python output back to C++ double/float? This way I would not have the problem of rounding errors when exchanging data between the two processes…

thx for the answers!

Answer 1

From the link you provided in your question (Additional Methods on Float):

This syntax is similar to the syntax
specified in section 6.4.4.2 of the
C99 standard, and also to the syntax
used in Java 1.5 onwards. In
particular, the output of float.hex()
is usable as a hexadecimal
floating-point literal in C or Java
code, and hexadecimal strings produced
by C’s %a format character or Java’s
Double.toHexString are accepted by
float.fromhex().

Example:

#include <cstdio>

int main() {
  float f = 42.79;
  printf("%.2f == %a\n", f, f);  
  fscanf(stdin, "%a", &f);
  printf("%.2f == %a\n", f, f);  
}

Run it:

$ g++ *.cpp && (python -c'print 12.34.hex()' | ./a.out )

Output:

42.79 == 0x1.5651ecp+5
12.34 == 0x1.8ae148p+3