13.4.1.1 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.