GNU C supports complex data types. You can declare both complex integer
types and complex floating types, using the keyword `__complex__`

.

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.

To extract the real part of a complex-valued expression `exp`, write
`__real__ `

. Likewise, use `exp``__imag__`

to
extract the imaginary part.

The operator ``~'` performs complex conjugation when used on a value
with a complex type.

GNU CC 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). None of the
supported debugging info formats has a way to represent noncontiguous
allocation like this, so GNU CC 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.

A future version of GDB will know how to recognize such pairs and treat them as a single variable with a complex type.

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