[expr.arith.conv] (original) (raw)

7 Expressions [expr]

7.4 Usual arithmetic conversions [expr.arith.conv]

Many binary operators that expect operands of arithmetic or enumeration type cause conversions and yield result types in a similar way.

The purpose is to yield a common type, which is also the type of the result.

This pattern is called the usual arithmetic conversions, which are defined as follows:

• The lvalue-to-rvalue conversion ([conv.lval]) is applied to each operand and the resulting prvalues are used in place of the original operands for the remainder of this section.
• If either operand is of scoped enumeration type ([dcl.enum]), no conversions are performed; if the other operand does not have the same type, the expression is ill-formed.
• Otherwise, if one operand is of enumeration type and the other operand is of a different enumeration type or a floating-point type, the expression is ill-formed.
• Otherwise, if either operand is of floating-point type, the following rules are applied:
  • If both operands have the same type, no further conversion is performed.
  • Otherwise, if one of the operands is of a non-floating-point type, that operand is converted to the type of the operand with the floating-point type.
  • Otherwise, if the floating-point conversion ranks ([conv.rank]) of the types of the operands are ordered but not equal, then the operand of the type with the lesser floating-point conversion rank is converted to the type of the other operand.
  • Otherwise, if the floating-point conversion ranks of the types of the operands are equal, then the operand with the lesser floating-point conversion subrank ([conv.rank]) is converted to the type of the other operand.
  • Otherwise, the expression is ill-formed.
• Otherwise, each operand is converted to a common type C.
  The integral promotion rules ([conv.prom]) are used to determine a type T1 and type T2 for each operand.47
  Then the following rules are applied to determine C:
  • If T1 and T2 are the same type, C is that type.
  • Otherwise, if T1 and T2 are both signed integer types or are both unsigned integer types,C is the type with greater rank.
  • Otherwise, let U be the unsigned integer type andS be the signed integer type.
    * If U has rank greater than or equal to the rank of S,C is U.
    * Otherwise, if S can represent all of the values of U,C is S.
    * Otherwise,C is the unsigned integer type corresponding to S.