The resulting value is truncated and stored in cresult. Because of integer promotions, however, c1, c2, and c3 are each converted to int, and the overall expression is successfully evaluated. Assuming that signed char is represented as an 8-bit value, the product of c1 and c2 (300) cannot be represented. The product of these values is then divided by the value of c3 (according to operator precedence rules). In this example, the value of c1 is multiplied by c2. The following code fragment shows the application of integer promotions: Integer promotions are applied as part of the usual arithmetic conversions to certain argument expressions operands of the unary +, -, and ~ operators and operands of the shift operators. If all values of the original type can be represented as an int, the value of the smaller type is converted to an int otherwise, it is converted to an unsigned int. Integer types smaller than int are promoted when an operation is performed on them. Prestandard C usually preferred to preserve signedness of the type. The intent of the rules is to ensure that the conversions result in the same numerical values and that these values minimize surprises in the rest of the computation. These rules include integer promotions, integer conversion rank, and the usual arithmetic conversions. The C integer conversion rules define how C compilers handle conversions. Conversion of an operand value to a compatible type causes no change to the value or the representation. Although conversions are generally required for the correct execution of a program, they can also lead to lost or misinterpreted data. Type-cast operator: allow implicit conversion to a particular type.Conversions can occur explicitly as the result of a cast or implicitly as required by an operation.Assignment operator: allow implicit conversion from a particular type on assignments.Single-argument constructors: allow implicit conversion from a particular type to initialize an object.In the world of classes, implicit conversions can be controlled by means of three member functions: Pointer upcast: pointers to a derived class can be converted to a pointer of an accessible and unambiguous base class, without modifying its const or volatile qualification.Pointers to any type can be converted to void pointers.Null pointers can be converted to pointers of any type.This warning can be avoided with an explicit conversion.įor non-fundamental types, arrays and functions implicitly convert to pointers, and pointers in general allow the following conversions: Some of these conversions may imply a loss of precision, which the compiler can signal with a warning. Otherwise, if the conversion is between numeric types of the same kind (integer-to-integer or floating-to-floating), the conversion is valid, but the value is implementation-specific (and may not be portable).If the result lies outside the range of representable values by the type, the conversion causes undefined behavior. If the conversion is from a floating-point type to an integer type, the value is truncated (the decimal part is removed).The conversions from/to bool consider false equivalent to zero (for numeric types) and to null pointer (for pointer types) true is equivalent to all other values and is converted to the equivalent of 1.If a negative integer value is converted to an unsigned type, the resulting value corresponds to its 2's complement bitwise representation (i.e., -1 becomes the largest value representable by the type, -2 the second largest.Other conversions between arithmetic types may not always be able to represent the same value exactly: Standard conversions affect fundamental data types, and allow the conversions between numerical types ( short to int, int to float, double to int.), to or from bool, and some pointer conversions.Ĭonverting to int from some smaller integer type, or to double from float is known as promotion, and is guaranteed to produce the exact same value in the destination type. Here, the value of a is promoted from short to int without the need of any explicit operator.
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