How to reduce repeated compilation in applications of the handle class

 

We know that when the header file on which a source file is dependent is modified, the source file needs to be re-compiled (the fragile base class problem). In order to introduce the method I will describe, let's take a look at a simple example. The Code is as follows:

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// Head. h

Struct

{Int I ;};

 

Class B

{

A *;

Public:

B (int n = 0 );

Void show ();

~ B ();

};

 

// Head. cpp

# Include "head. h"

# Include <iostream. h>

B: B (int n)

{

A = new;

A-> I = n;

}

Void B: show ()

{

Cout <a-> I;

}

B ::~ B ()

{

Delete;

}

 

// Main. cpp

# Include <iostream>

# Include "head. h"

Using namespace std;

Int main ()

{

B B (1 );

B. show ();

Return 1;

}

If we want to modify the struct A, for example, we need to add A member variable to A, then head. h is changed to include its head. cpp and main. cpp both need to be re-compiled.

We know that Class B is A handle class that encapsulates Class A. In this form, how can we modify the code so that the definition of Class A can be reduced and re-compiled?

After observing head. h, we found that Class A does not need to be fully defined in the Declaration process of Class B. We Can slightly modify the code using this point. The modified code is as follows:

 

// Head. h

Class B

{

Struct A; // incomplete class type description

A *;

Public:

B (int n = 0 );

Void show ();

~ B ();

};

 

// Head. cpp

# Include "head. h"

# Include <iostream. h>

Struct B: full definition of A //

{

Int I;

};

B: B (int n)

{

A = new;

A-> I = n;

}

Void B: show ()

{

Cout <a-> I;

}

B ::~ B ()

{

Delete;

}

 

// Main. cpp

# Include <iostream>

# Include "head. h"

Using namespace std;

Int main ()

{

B B (1 );

B. show ();

Return 1;

}

After this modification, if we need to modify the definition of A, we only need to modify head. cpp to avoid the need to redefine main. cpp.

 

Conclusion: if there is a handle class in our system and the system is very large, we may need this so-called trick to avoid excessive Compilation Time.

Author: yucan1001