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| Flow control | ||||||||||||||||
| Conditional execution statements | ||||||||||||||||
| Iteration statements (loops) | ||||||||||||||||
| Jump statements | ||||||||||||||||
| Functions | ||||||||||||||||
| Function declaration | ||||||||||||||||
| Lambda function expression | ||||||||||||||||
inline specifier | ||||||||||||||||
| Dynamic exception specifications(until C++17*) | ||||||||||||||||
noexcept specifier(C++11) | ||||||||||||||||
| Exceptions | ||||||||||||||||
| Namespaces | ||||||||||||||||
| Types | ||||||||||||||||
| Specifiers | ||||||||||||||||
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| Storage duration specifiers | ||||||||||||||||
| Initialization | ||||||||||||||||
| Expressions | ||||||||||||||||
| Alternative representations | ||||||||||||||||
| Literals | ||||||||||||||||
| Boolean -Integer -Floating-point | ||||||||||||||||
| Character -String -nullptr(C++11) | ||||||||||||||||
| User-defined(C++11) | ||||||||||||||||
| Utilities | ||||||||||||||||
| Attributes(C++11) | ||||||||||||||||
| Types | ||||||||||||||||
typedef declaration | ||||||||||||||||
| Type alias declaration(C++11) | ||||||||||||||||
| Casts | ||||||||||||||||
| Memory allocation | ||||||||||||||||
| Classes | ||||||||||||||||
| Class-specific function properties | ||||||||||||||||
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| Special member functions | ||||||||||||||||
| Templates | ||||||||||||||||
| Miscellaneous | ||||||||||||||||
A constructor that is not declared with the specifierexplicitand which can be called with a single parameter(until C++11) is called aconverting constructor.
Unlike explicit constructors, which are only considered duringdirect initialization (which includesexplicit conversions such asstatic_cast), converting constructors are also considered duringcopy initialization, as part ofuser-defined conversion sequence.
It is said that a converting constructor specifies an implicit conversion from the types of its arguments (if any) to the type of its class. Note that non-explicituser-defined conversion function also specifies an implicit conversion.
Implicitly-declared and user-defined non-explicitcopy constructors andmove constructors are converting constructors.
struct A{ A(){}// converting constructor (since C++11) A(int){}// converting constructor A(int,int){}// converting constructor (since C++11)}; struct B{explicit B(){}explicit B(int){}explicit B(int,int){}}; int main(){ A a1=1;// OK: copy-initialization selects A::A(int) A a2(2);// OK: direct-initialization selects A::A(int) A a3{4,5};// OK: direct-list-initialization selects A::A(int, int) A a4={4,5};// OK: copy-list-initialization selects A::A(int, int) A a5=(A)1;// OK: explicit cast performs static_cast, direct-initialization // B b1 = 1; // error: copy-initialization does not consider B::B(int) B b2(2);// OK: direct-initialization selects B::B(int) B b3{4,5};// OK: direct-list-initialization selects B::B(int, int)// B b4 = {4, 5}; // error: copy-list-initialization selected an explicit constructor// B::B(int, int) B b5=(B)1;// OK: explicit cast performs static_cast, direct-initialization B b6;// OK, default-initialization B b7{};// OK, direct-list-initialization// B b8 = {}; // error: copy-list-initialization selected an explicit constructor// B::B() [](...){}(a1, a4, a4, a5, b5);// may suppress "unused variable" warnings}
