Class implementation file

Using this structure, a class definition file containing the declaration of the class and its members is also created. If the class definition has been included and the implementation file for its methods is available, the user can instantiate an object of the class. The purpose of this structure is to keep the implementation code hidden, but allow the user to view the design.[2][3]

Users make use of the public interface of an object so as to make creating objects as simple as possible, ensuring that client code does not distract the user with unnecessary details of the class's implementation.[4] This allows the user the information needed to use the class effectively, but prevents him or her from damaging the compiled code.[5]

An implementation file is used in C++ programming when creating a class definition to split the interface from the implementation. The header file would declare all the member functions (methods) and data methods (fields) that the class has.[6][7][8]

The implementation file will contain the actual definition or source code of the methods declared in the header file. This file can start with a header block, which provides comments that describe the purpose of the defined class and any details about the creation of the actual file, such as the author of the file and date the file was created.[9] It can also include any libraries from the C++ Standard Library that will be used by any of the declared methods in the file. The class implementation file will usually have a line to include the associated header file (see examples below).

#include "example_class.h"

ExampleClass::ExampleClass() = default;

void ExampleClass::AddSomething(int k) {
   ...
}

#include <string>

class ExampleClass {
 public:
  ExampleClass();  // Constructor.
  void AddSomething(int k);          

 private:
  std::string name_;                      
};

#import <UIKit/UIKit.h>

@interface ExampleClass : NSObject {
    // instance variable declarations go here
}
- (NSString*) name;
@end

#import "ExampleClass.h"

@implementation ExampleClass
- (NSString*) name {
    return @"…";
}
@end

• C++ classes
• Header file
• Source code
• C++ Standard Library
• Objective-C

• Header File and Implementation File