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Implicit type conversion, also known as coercion or type juggling, is an automatic type conversion by the compiler. Some programming languages allow compilers to provide coercion; others require it. In a mixed-type expression, data of one or more subtypes can be converted to a supertype as needed at runtime so that the program will run correctly.
There are many examples of languages that allow implicit type conversions, but in a type-safe manner. For example, both C++ and C# allow programs to define operators to convert a value from one type to another with well-defined semantics. When a C++ compiler encounters such a conversion, it treats the operation just like a function call.
The process of verifying and enforcing the constraints of types—type checking—may occur at compile time (a static check) or at run-time (a dynamic check). If a language specification requires its typing rules strongly, more or less allowing only those automatic type conversions that do not lose information, one can refer to the process as strongly typed; if not, as weakly typed.
C++ enforces stricter typing rules (no implicit violations of the static type system [1]), and initialization requirements (compile-time enforcement that in-scope variables do not have initialization subverted) [7] than C, and so some valid C code is invalid in C++. A rationale for these is provided in Annex C.1 of the ISO C++ standard.
It would be possible to infer the types of all the variables at compile time. In the example above, the compiler would infer that result and x have type integer since the constant 1 is type integer, and hence that add_one is a function int -> int. The variable result2 isn't used in a legal manner, so it wouldn't have a type.
While we could also convert myObject to a compile-time String using the universal java.lang.Object.toString(), this would risk calling the default implementation of toString() where it was unhelpful or insecure, and exception handling could not prevent this. In C++, run-time type checking is implemented through dynamic_cast.
Conversion constructors provide a means for a compiler to implicitly create an object belonging to one class based on an object of a different type. These constructors are usually invoked implicitly to convert arguments or operands to an appropriate type, but they may also be called explicitly.
Most C code can easily be made to compile correctly in C++ but there are a few differences that cause some valid C code to be invalid or behave differently in C++. For example, C allows implicit conversion from void * to other pointer types but C++ does not (for type safety reasons).