15.4.1.1 C and C++ Operators
Operators must be defined on values of specific types. For instance,
+
is defined on numbers, but not on structures. Operators are
often defined on groups of types.
For the purposes of C and C++, the following definitions hold:
- Integral types include
int
with any of its storage-class
specifiers; char
; enum
; and, for C++, bool
.
- Floating-point types include
float
, double
, and
long double
(if supported by the target platform).
- Pointer types include all types defined as
(
type *)
.
- Scalar types include all of the above.
The following operators are supported. They are listed here
in order of increasing precedence:
,
- The comma or sequencing operator. Expressions in a comma-separated list
are evaluated from left to right, with the result of the entire
expression being the last expression evaluated.
=
- Assignment. The value of an assignment expression is the value
assigned. Defined on scalar types.
- op
=
- Used in an expression of the form a
op=
b,
and translated to a =
a op b.
op=
and =
have the same precedence.
op is any one of the operators |
, ^
, &
,
<<
, >>
, +
, -
, *
, /
, %
.
?:
- The ternary operator. a
?
b :
c can be thought
of as: if a then b else c. a should be of an
integral type.
||
- Logical or. Defined on integral types.
&&
- Logical and. Defined on integral types.
|
- Bitwise or. Defined on integral types.
^
- Bitwise exclusive-or. Defined on integral types.
&
- Bitwise and. Defined on integral types.
==
, !=
- Equality and inequality. Defined on scalar types. The value of these
expressions is 0 for false and non-zero for true.
<
, >
, <=
, >=
- Less than, greater than, less than or equal, greater than or equal.
Defined on scalar types. The value of these expressions is 0 for false
and non-zero for true.
<<
, >>
- left shift, and right shift. Defined on integral types.
@
- The gdb “artificial array” operator (see Expressions).
+
, -
- Addition and subtraction. Defined on integral types, floating-point types and
pointer types.
*
, /
, %
- Multiplication, division, and modulus. Multiplication and division are
defined on integral and floating-point types. Modulus is defined on
integral types.
++
, --
- Increment and decrement. When appearing before a variable, the
operation is performed before the variable is used in an expression;
when appearing after it, the variable's value is used before the
operation takes place.
*
- Pointer dereferencing. Defined on pointer types. Same precedence as
++
.
&
- Address operator. Defined on variables. Same precedence as
++
.
For debugging C++, gdb implements a use of `&' beyond what is
allowed in the C++ language itself: you can use `&(&ref)'
to examine the address
where a C++ reference variable (declared with `&ref') is
stored.
-
- Negative. Defined on integral and floating-point types. Same
precedence as
++
.
!
- Logical negation. Defined on integral types. Same precedence as
++
.
~
- Bitwise complement operator. Defined on integral types. Same precedence as
++
.
.
, ->
- Structure member, and pointer-to-structure member. For convenience,
gdb regards the two as equivalent, choosing whether to dereference a
pointer based on the stored type information.
Defined on
struct
and union
data.
.*
, ->*
- Dereferences of pointers to members.
[]
- Array indexing. a
[
i]
is defined as
*(
a+
i)
. Same precedence as ->
.
()
- Function parameter list. Same precedence as
->
.
::
- C++ scope resolution operator. Defined on
struct
, union
,
and class
types.
::
- Doubled colons also represent the gdb scope operator
(see Expressions). Same precedence as
::
,
above.
If an operator is redefined in the user code, gdb usually
attempts to invoke the redefined version instead of using the operator's
predefined meaning.