Studio:Scl brew class: Difference between revisions
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The C-based class must adhere to the following rules: | The C-based class must adhere to the following rules: | ||
* The class is structured using a C structure typedef | * The class is structured using a C structure typedef | ||
* [[Function pointers]] are used to define the class methods | * [[Category:Function_Pointers|Function pointers]] are used to define the class methods | ||
* Each class method is required to have a parameter, which is used to pass in a reference to the object upon which the method will act | * Each class method is required to have a parameter, which is used to pass in a reference to the object upon which the method will act | ||
* There must be at least one SCL-compliant function that references the class typedef. | * There must be at least one SCL-compliant function that references the class typedef. |
Revision as of 20:59, 21 August 2008
The scl_brew_class pragma
The scl_brew_class pragma is for Brew API developers who simulate C++ classes and virtual functions within ANSI C by following a fixed set of conventions. The conventions are used to create classes referred to as "Brew Classes." A Brew class is formed from a C structure type that is used to represent the C++ virtual function table. The structure must contain members which are of the type pointer to function. Furthermore, these members must point to a function type whose first parameter is a pointer to this same structure type.
The C-based class must adhere to the following rules:
- The class is structured using a C structure typedef
- are used to define the class methods
- Each class method is required to have a parameter, which is used to pass in a reference to the object upon which the method will act
- There must be at least one SCL-compliant function that references the class typedef.
Syntax
#pragma scl_brew_class(structure-name)
#pragma scl_brew_class(structure-name, field-name 1 .. n)
Parameters | Type | Description |
structure-name | Type | Name of the structure that defines the C-based class |
field-name 1 .. n | Member | Name of the field that defines one or more methods |
Notes
The method names are automatically generated based on the class name and field name as follows:
<class-name>_<field-name>
For additional information on scl_brew_class, including constraints, refer to the section on scl_brew_class in the [STRIDE SCL Reference Guide].
Example
// Const defining a maximum string length // #define MAX_STR_SIZE 64 // Structure type used to define a C-based class. Each // // method is defined as a pointer to a function whose // // first parameter is a pointer to the structure type. // typedef struct _myObj MyObj; struct _myObj { int ( *method1 )(MyObj * t, int x, int y); void ( *method2 )(MyObj * t, char * str); char* ( *method3 )(MyObj * t); }; // createMyObj - Interface used to instantiate the C-based object. // // *ppObj will be declared as opaque to obtain the object's address. // // The object's address can then be passed in as the first // // parameter for each of the method calls. // void createMyObj (MyObj ** ppObj); static MyObj * bindMyObj(void * pObj) { return (MyObj *) pObj; }; #ifdef _SCL // Use the scl_function pragma to associate an object with the // // interface. // // Use the scl_ptr pragma to define the parameter ppObj as an OUT // // pointer. // // Use the scl_ptr_opaque pragma to opaque the child pointer to the // // object. // #pragma scl_function(createMyObj) #pragma scl_ptr(createMyObj, ppObj, OUT, PRIVATE) #pragma scl_ptr_opaque(createMyObj, *ppObj) // Use the scl_function pragma to associate an object with the interface // #pragma scl_function(bindMyObj) #pragma scl_brew_class(MyObj) // Use the scl_string pragma to declare the char pointers as ASCII strings. // // The method names are derived from <class-name>, <field-name> // #pragma scl_string(MyObj_method2, str, MAX_STR_SIZE) #pragma scl_string(MyObj_method3(), MAX_STR_SIZE) #endif //_SCL//