What is the difference between static_cast<> an

问题:

Is there any reason to prefer static_cast<> over C style casting? Are they equivalent? Is their any sort of speed difference?

回答1:

C++ style casts are checked by the compiler. C style casts aren\'t and can fail at runtime

also, c++ style casts can be searched for easily, whereas it\'s really hard to search for c style casts

Another big benefit is that the 4 different C++ style casts express the intent of the programmer more clearly.

When writing C++ I\'d pretty much always use the C++ ones over the the C style.

回答2:

In short:

1. static_cast<>() gives you a compile time checking ability, C-Style cast doesn\'t.
2. static_cast<>() is more readable and can be spotted easily anywhere inside a C++ source code, C_Style cast is\'nt.
3. Intentions are conveyed much better using C++ casts.

More Explanation:

The static cast performs conversions between compatible types. It is similar to the C-style cast, but is more restrictive. For example, the C-style cast would allow an integer pointer to point to a char.

char c = 10;       // 1 byte
int *p = (int*)&c; // 4 bytes

Since this results in a 4-byte pointer ( a pointer to 4-byte datatype) pointing to 1 byte of allocated memory, writing to this pointer will either cause a run-time error or will overwrite some adjacent memory.

*p = 5; // run-time error: stack corruption

In contrast to the C-style cast, the static cast will allow the compiler to check that the pointer and pointee data types are compatible, which allows the programmer to catch this incorrect pointer assignment during compilation.

int *q = static_cast<int*>(&c); // compile-time error

You can also check this page on more explanation on C++ casts : Click Here

回答3:

struct A {};
struct B : A {};
struct C {}; 

int main()
{
    A* a = new A;    

    int i = 10;

    a = (A*) (&i); // NO ERROR! FAIL!

    //a = static_cast<A*>(&i); ERROR! SMART!

    A* b = new B;

    B* b2 = static_cast<B*>(b); // NO ERROR! SMART!

    C* c = (C*)(b); // NO ERROR! FAIL!

    //C* c = static_cast<C*>(b); ERROR! SMART!
}

回答4:

See A comparison of the C++ casting operators.

However, using the same syntax for a variety of different casting operations can make the intent of the programmer unclear.

Furthermore, it can be difficult to find a specific type of cast in a large codebase.

the generality of the C-style cast can be overkill for situations where all that is needed is a simple conversion. The ability to select between several different casting operators of differing degrees of power can prevent programmers from inadvertently casting to an incorrect type.

回答5:

static_cast checks at compile time that conversion is not between obviously incompatible types. Contrary to dynamic_cast, no check for types compatibility is done at run time. Also, static_cast conversion is not necessarily safe.

static_cast is used to convert from pointer to base class to pointer to derived class, or between native types, such as enum to int or float to int.

The user of static_cast must make sure that the conversion is safe.

The C-style cast does not perform any check, either at compile or at run time.

回答6:

Since there are many different kinds of casting each with different semantics, static_cast<> allows you to say \"I\'m doing a legal conversion from one type to another\" like from int to double. A plain C-style cast can mean a lot of things. Are you up/down casting? Are you reinterpreting a pointer?

回答7:

A great post explaining different casts in C/C++, and what C-style cast really does: https://anteru.net/blog/2007/12/18/200/index.html

C-Style casting, using the (type)variable syntax. The worst ever invented. This tries to do the following casts, in this order: (see also C++ Standard, 5.4 expr.cast paragraph 5)

1. const_cast
2. static_cast
3. static_cast followed by const_cast
4. reinterpret_cast
5. reinterpret_castfollowed by const_cast