WARNING
The
following examples remove the default entry point function when all default
libraries are removed. The default entry point handles the initialization of
the C run-time library (calling the _CRT_INIT function), and executes
C++ constructors for static objects. It will now be up to the application to
perform these tasks.
Getting Started
 To get started on creating small
applications a new configuration should be added to the main project to
not break the current working Debug and Release
configurations. To create a new configuration select
Configurations... from the Build menu. Click the
Add button. The Add Project Configuration dialog will be
displayed. In the Configuration edit box type the new name of the
configuration. In the Copy Settings from combo box select the
Win32 Release configuration.
After adding the new
configuration it must select as the current configuartion. To do so
select Set active configuration... from the Build menu.
The Set Active Project Configuration, will be displayed. Select
the new configuration and click OK.
Now that the configuartion is
set we may alter the compiler and linker options without worrying about
breaking the project. |
Compiler Options
To make this configuration
unique for the preprocessor it is recommended that you added a global
preprocessor definition. To do so add the following option in the Project
Options under C/C++ settings: /D _TINYCONFIG
One
of the options to change here is to set the optimizations to Minimize
Size. To do so change the following option in the Project Options
under C/C++ settings: /O1
The
only other option to consider is the structure member alignment. The default
alignment is 8 bytes, by changing this to 1 byte the structure members will be
tightly packed in memory, although once in memory they will be slower. To
change the structure member alignment add the following line to the Project
Options under C/C++ settings, where n is 1, 2, 4, 8, or 16: /Zp[n]
Linker Options
The main objective is to get rid of all
libraries we do not need, this means clib. By removing clib you will not be
able to use the standard C library, which means the code will not be portable
across operating systems. To get rid of all default libraries select
Project -> Settings from the main menu and click on the Link
tab. Check the Ignore all default libraries check box. As this will get
rid of all standard C functions we need to find alternatives in the Win32 API,
luckily they exist. See the function list below. Now get rid of any library
that you do not need from the Object/library modules edit box.
To disable the use of all default libraries add the following line to
the Project Options under linker settings: /NODEFAULTLIB
Incremental
linking must also be disabled by adding the following line: /INCREMENTAL:NO
Microsoft
Visual C++ uses a default file alignment of 4KB instead of the default 512
bytes. When reduced to 512 bytes the size of the application falls
significantly. Although a file alignment of 4KB loads faster on Windows 98 and
reduces file swapping. To change the alignment to 512 bytes add the following
line to the Project Options under linker settings: /OPT:NOWIN98
An
alternative is to define the exact file alignment: /ALIGN:512
Although
this parameter will cause the following linker warning: LINK : warning LNK4108: /ALIGN specified without /DRIVER or /VXD; image may not run
Merging
sections together will result in a smaller overall application. To view the
names of the sections in your application use the DUMPBIN tool with the
/SUMMARY parameter. For instance you can merge the relocation data (.rdata)
and the text (.text) sections. To merge sections add the following line to the
Project Options under linker settings: /MERGE:[from]=[to]
If
you changed the default name of the entry point you will need to tell the
linker the new name of the entry point. Add the following line to the
Project Options under linker settings: /ENTRY:[function name]
Executables
When we remove the Default
Libraries we also remove a hidden function that Microsoft Visual C++
provides. This function serves as the entry point to an executable. The name
of the function that Microsoft Visual C++ uses as the entry point is called
WinMainCRTStartup. To make life easier this article will use the same
name for the entry point. If you wish to change the entry point function name
see Linker
Options above.
The application will have to supply its own entry
point that calls WinMain. The entry point prototype is as follows: int WINAPI WinMainCRTStartup(void);
Unlike
WinMain this function does not take any parameters, therefore it's up
to the application to provide the information when calling WinMain. The
four parameters that WinMain takes are: HINSTANCE hInstance,
HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow.
All these can easily be retrieved through standard Win32 API. The
hInstance parameter can be retrieved by calling GetModuleHandle.
The hPrevInstance parameter is ignored in Win32. The lpCmdLine
parameter can be retrieved by calling GetCommandLine. The
nCmdShow parameter is a bit more complex, but all it requires is one
call to GetStartupInfo. The main file of your application should now
look something like the following code:
[09-03-01] The following code has been updated and is based
mainly on CRT0TWIN.C by Matt Pietrek 1996. Thanks goes out to Florian Blümel
for pointing this out.
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR szCmdLine,int iCmdShow)
{
...
return 0;
}
#ifdef _TINYCONFIG
int WINAPI WinMainCRTStartup(void)
{
STARTUPINFO StartupInfo={sizeof(STARTUPINFO),0};
int mainret;
char *lpszCommandLine = GetCommandLine();
// skip past program name (first token in command line).
if( *lpszCommandLine == '"' ) // check for and handle quoted program name
{
// scan, and skip over, subsequent characters until another
// double-quote or a null is encountered
while( *lpszCommandLine && (*lpszCommandLine != '"') )
lpszCommandLine++;
// if we stopped on a double-quote (usual case), skip over it.
if( *lpszCommandLine == '"' )
lpszCommandLine++;
}
else
{
// first token wasn't a quote
while ( *lpszCommandLine > ' ' )
lpszCommandLine++;
}
// skip past any white space preceeding the second token.
while ( *lpszCommandLine && (*lpszCommandLine <= ' ') )
lpszCommandLine++;
GetStartupInfo(&StartupInfo);
mainret = WinMain( GetModuleHandle(NULL),
NULL,
lpszCommandLine,
StartupInfo.dwFlags & STARTF_USESHOWWINDOW
? StartupInfo.wShowWindow : SW_SHOWDEFAULT );
ExitProcess(mainret);
return mainret;
}
#endif
Dynamically Linked Libraries
When we remove the Default Libraries we also remove a hidden
function that Microsoft Visual C++ provides. This function serves as the entry
point to the dynamically linked library. The name of the function that
Microsoft Visual C++ uses as the entry point is called
_DllMainCRTStartup. To make life easier this article will use the same
name for the entry point. If you wish to change the entry point function name
see Linker
Options above.
The application will have to supply its own entry
point. The entry point prototype is as follows: BOOL WINAPI _DllMainCRTStartup(HINSTANCE hinstDLL,DWORD fdwReason,LPVOID lpReserved);
As
you can see the entry point function takes exactly the same parameters as
DllMain. At first glance getting rid of the DllMain function
seems like the logical thing to do, unfortunately the Debug and
Release configurations require DllMain to exist. A solution is
shown below. An alternative to this would be to create only a DllMain
and change the ENTRY Linker Option
for this configuration to DllMain. BOOL WINAPI DllMain(HINSTANCE hinstDLL,DWORD fdwReason,LPVOID lpReserved)
{
switch( fdwReason )
{
...
}
return 1;
}
#ifdef _TINYCONFIG
BOOL WINAPI _DllMainCRTStartup(HINSTANCE hinstDLL,DWORD fdwReason,LPVOID lpReserved)
{
return DllMain(hinstDLL,fdwReason,lpReserved);
}
#endif
Add these files to your project. Select
Project -> Settings from the main menu, click on the
C/C++ tab, and choose Precompiled Headers from the
Category combo box. Highlight the project in the left hand side tree
view. Select Automatic use of precompiled headers and in the
Through header edit box write the name of the main header. Then
select the new source file form the tree view and choose Create
precompiled header file (.pch). In the Through Header edit
box write the name of the main header file.