Aug 042008

Well what is deprecation? It’s just a way to tell the user that a better/safer function is available for a function which he is using!

For e.g. strcpy.

If you use strcpy in VC8 we’ll get a warning saying that it’s deprecated, instead use strcpy_s which is the secure version of this API.

So the question is how to deprecate a function using VC++ compiler. There are two options in VC++…

  1. Using __declspec(deprecated)
  2. Using #pragma deprecated

Using __declspec(deprecated) compiler directive.

// Helper #defines for deprecation compiler directive
#define deprecate __declspec(deprecated)
#define deprecate_msg(message) __declspec(deprecated(message))

First version is just plain, just produces default compiler warnings, while second version prints out a custom message along with the normal deprecation message.

// Deprecate a function
void deprecate OldFunction() {}

// Deprecate a class/struct
class deprecate OldClass {};

// This time with custom message //

// Deprecate a function, also tell the user that a better option exists
deprecate_msg( "******OldFunction is deprecated, start using NewFunction******" )
// Deprecate a class/struct, also tell the user that a better option exists
deprecate_msg( "******OldClass is deprecated, start using NewClass******" )

The output that I get looks like this

\consolegunieapig\consolegunieapig.cpp(144) : warning C4996: ‘OldFunction’ was declared deprecated
1> \consolegunieapig\consolegunieapig\consolegunieapig.cpp(124) : see declaration of ‘OldFunction’
1>        Message: ‘******OldFunction is deprecated, start using NewFunction******’
1>\consolegunieapig\consolegunieapig\consolegunieapig.cpp(145) : warning C4996: ‘OldClass’ was declared deprecated
1>\consolegunieapig\consolegunieapig\consolegunieapig.cpp(128) : see declaration of ‘OldClass’
1>        Message: ‘******OldClass is deprecated, start using NewClass******’

Using #pragma deprecated

Another option to deprecate a class/struct/function is to use the #pragma deprecated compiler directive.

The main difference is that using __declspec(deprecated) we can selective deprecate functions but with #pragma deprecated every function with that particular name is marked as deprecated. With #pragma deprecated you can even deprecate a macro.

This is how we use #pragma deprecated

void OldFunction() {}
void OldFunction( int i ) {}
class OldClass {};

// Note that both versions of OldFunction will be marked as deprecated.
#pragma deprecated(OldFunction,OldClass);
May 042008

The compiler generates prolog and epilogue code for functions compiled for do some additional housekeeping for try/catch blocks, maintaining stack frame etc.

So what to do to prevent such code generation in MS VC compiler! MSVC compiler provides us with an attribute called __declspec(naked). Use this to prevent code generation by VC compiler.

Note that naked attribute can only be specified on function definitions and not on declarations, also it cannot be specified for data declarations!

An e.g.

__declspec(naked) void SomeFunc()
    // Some code

Well what’s the use of this! You can write your own prologue or epilogue code. MSDN also mentions that this is useful for virtual device driver development!