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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:

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 opb, 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.