Re: About the GCC

[Andrew Haley <aph at redhat dot com>]

Christian Schoenebeck writes:
 > Am Donnerstag, 27. April 2006 11:20 schrieb zerenz@itu.edu.tr:
 > >   We want to compile a Fluent UDF function in which we need to define a
 > > complex variable. However we couldnt find how to. Could you please show us
 > > a way?
 > 
 > Now as you say it, I thought I remembered a "complex" type gcc extension as 
 > well, but couldn't find it either.

TFM!  :-)

5.9 Complex Numbers

ISO C99 supports complex floating data types, and as an extension GCC
supports them in C89 mode and in C++, and supports complex integer data
types which are not part of ISO C99.  You can declare complex types
using the keyword `_Complex'.  As an extension, the older GNU keyword
`__complex__' is also supported.

 For example, `_Complex double x;' declares `x' as a variable whose
real part and imaginary part are both of type `double'.  `_Complex
short int y;' declares `y' to have real and imaginary parts of type
`short int'; this is not likely to be useful, but it shows that the set
of complex types is complete.

 To write a constant with a complex data type, use the suffix `i' or
`j' (either one; they are equivalent).  For example, `2.5fi' has type
`_Complex float' and `3i' has type `_Complex int'.  Such a constant
always has a pure imaginary value, but you can form any complex value
you like by adding one to a real constant.  This is a GNU extension; if
you have an ISO C99 conforming C library (such as GNU libc), and want
to construct complex constants of floating type, you should include
`<complex.h>' and use the macros `I' or `_Complex_I' instead.

 To extract the real part of a complex-valued expression EXP, write
`__real__ EXP'.  Likewise, use `__imag__' to extract the imaginary
part.  This is a GNU extension; for values of floating type, you should
use the ISO C99 functions `crealf', `creal', `creall', `cimagf',
`cimag' and `cimagl', declared in `<complex.h>' and also provided as
built-in functions by GCC.

 The operator `~' performs complex conjugation when used on a value
with a complex type.  This is a GNU extension; for values of floating
type, you should use the ISO C99 functions `conjf', `conj' and `conjl',
declared in `<complex.h>' and also provided as built-in functions by
GCC.

 GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa).  Only the DWARF2
debug info format can represent this, so use of DWARF2 is recommended.
If you are using the stabs debug info format, GCC describes a
noncontiguous complex variable as if it were two separate variables of
noncomplex type.  If the variable's actual name is `foo', the two
fictitious variables are named `foo$real' and `foo$imag'.  You can
examine and set these two fictitious variables with your debugger.

Andrew.