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 aop= 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)'
(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 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.
Debugging with GDB