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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 section 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)'
(or, if you prefer, simply `&&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 section 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.
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