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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