Menu
This answer says:
… Finally,
typedef struct { ... } Foo;declares an anonymous structure and creates a typedef for it. Thus, with this construct, it doesn't have a name in the tag namespace, only a name in the typedef namespace. This means it also can't be forward-declared. If you want to make a forward declaration, you have to give it a name in the tag namespace.
What is forward declaration?
629
In C++, Forward declarations are usually used for Classes. In this, the class is pre-defined before its use so that it can be called and used by other classes that are defined before this. Example: // Forward Declaration class A class A; // Definition of class A class A{ // Body };
A forward declaration allows us to tell the compiler about the existence of an identifier before actually defining the identifier. In the case of functions, this allows us to tell the compiler about the existence of a function before we define the function's body.
Forward declarations in C++ are useful to save in compile time as the compiler does not need to check for translation units in the included header. Also it has other benefits such as preventing namespace pollution, allowing to use PImpl idiom and it may even reduce the binary size in some cases.
The Google style guide recommends against using forward declarations, and for good reasons: If someone forward declares something from namespace std, then your code exhibits undefined behavior (but will likely work).
Chad has given a pretty good dictionary definition. Forward declarations are often used in C++ to deal with circular relationships. For example:
class B; // Forward declaration
class A
{
B* b;
};
class B
{
A* a;
};
"In computer programming, a forward declaration is a declaration of an identifier (denoting an entity such as a type, a variable, or a function) for which the programmer has not yet given a complete definition."
-Wikipedia
32
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
