Debugging with GDB: C Operators

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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:

- 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. The operator op is any one of the operators `|`, `^`, `&`, `<<`, `>>`, `+`, `-`, `*`, `/`, `%`.

`?:`

  The ternary operator. `a ? b : c` can be thought of as: if a then b else c. The argument 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.

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