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Last update Fri Jun 4 11:04:58 2010

Switching to Digital Mars C++

Digital Mars C++ offers numerous advantages over other compilers, both in programmer productivity and in the speed and robustness of generated code. Switching to Digital Mars C++ is well worth the effort. This chapter outlines general considerations for converting existing code.

What's in This Chapter


Portable Programming Practices

Some of the programming practices that help make code portable and reusable also help make it compatible with Digital Mars C++. Your code will be easier to convert if you:

Object Level Compatibility

Digital Mars C++ object modules are "broadly compatible" with Microsoft and Borland objects. However, there are some differences:

Using Third-Party Libraries

If you must use third-party libraries written for Microsoft or Borland C++ with the Digital Mars C++ compiler, there is no simple way to determine which features are compatible. Your code could even link correctly and still contain obscure errors.

If you have the source to the third-party library, try recompiling it with Digital Mars C++. A better solution is to obtain the Digital Mars version of the library from the vendor. Recompiling for Digital Mars C++ In many cases, converting programs written for another compiler to Digital Mars C++ can be as easy as recompiling them. Here are some steps you can take to ease recompilation:

Compile time warnings

By default, the Digital Mars C++ compiler generates warnings in response to more conditions than do most other compilers. If you find these unfamiliar warnings annoying, compile with the -w (warning level) option. Each instance of -w on the SC command line turns off a specific warning. For example, the command:
dmc -w2 -w6 myfile.cpp 
turns off warnings number 2 and 6. For information on warnings and their numbers, see Compiling Code.

Converting from Microsoft

This chapter describes differences you should consider when converting code written for Microsoft Visual C++ Version 1.5 to Digital Mars C++.

What's in This Chapter

This chapter discusses compatibility issues between Microsoft Visual C++ and Digital Mars C++ with respect to these issues:

Keywords

Digital Mars C++ supports most of Microsoft C's nonstandard keywords. The following table lists Microsoft's keyword extensions and their Digital Mars counterparts:

Table 23-1 Support for Microsoft keywords
Unsupported Microsoft keywords
__fastcall
__fortran
__saveregs
__segment
__segname
__self

Predefined Macros

Digital Mars C++ supports most of Microsoft C's nonstandard macros. The following table lists Microsoft's extended macros and their Digital Mars counterparts:

Table 23-2 Support for Microsoft C nonstandard macros
Unsupported Microsoft macros Digital Mars counterparts
_CHAR_UNSIGNED _CHAR_UNSIGNED
_FAST No support
_MSC_VER __DMC__ (works the same, but version numbers are for SC)
_MSDOS Recommended use is as a command line argument
MSDOS Recommended use is as a command line argument
_PCODE No support
_QC No support
M_I286 M_I286
M_I386 M_I386
M_I8086 M_I8086
M_I86 M_I86
M_I86CM M_I86CM
M_I86HM No support
M_I86LM M_I86LM
M_I86MM M_I86MM
M_I86SM M_I86SM
M_I86TM M_I86TM

Header Files

The Digital Mars C++ run-time library includes all the Microsoft nonstandard headers. Many of these headers simply reference the Digital Mars header file that contains equivalent functions. Digital Mars C++ issues a warning whenever your code makes use of such a header file. In general, we recommend switching to ANSI-compliant headers wherever possible.

Library Functions

Digital Mars C++ supports the great majority of Microsoft Visual C++ Version 1.5 library functions. The table below lists the only Microsoft functions that the Digital Mars C++ run-time library does not support:

Table 23-3 Unsupported Microsoft library functions
Unsupported functions Microsoft header Comments
Graphics functions graph.h Digital Mars C++ does not support the DOS graphics system.
Charting functions pgchart.h  
Virtual memory functions vmemory.h Digital Mars C++ no longer supports Virtual Code Management (VCM).
QuickWin functions io.h  
_bexpand malloc.h Use farrealloc instead.
_bfree malloc.h  
_bfreeseg malloc.h  
_bheapadd malloc.h Not needed with Digital Mars C++ heap management.
_bheapchk malloc.h  
_bheapmin malloc.h  
_bheapseg malloc.h  
_bheapset malloc.h  
_bheapwalk malloc.h  
_bmalloc malloc.h  
_bmsize malloc.h  
_brealloc malloc.h  
_dieeetomsbin math.h  
_dmsbintoieee math.h  
_expand malloc.h Use realloc instead.
_fexpand malloc.h Use farrealloc instead.
_fheapchk malloc.h  
_fheapmin malloc.h  
_fheapset malloc.h  
_fheapwalk malloc.h  
_fieeetomsbin math.h  
_fmsbintoieee math.h  
_heapadd malloc.h Not needed with Digital Mars C++ heap management.
_heapchk malloc.h  
_heapmin malloc.h  
_heapset malloc.h  
_heapwalk malloc.h  
_j0, _j1, _jnl math.h  
_j0l, _j1l, _jn math.h  
_nexpand malloc.h Use realloc instead.
_nheapadd malloc.h Not needed with Digital Mars C++ heap management.
_nheapchk malloc.h  
_nheapmin malloc.h  
_nheapset malloc.h  
_nheapwalk malloc.h  
_setbnew_handler new.h  
_sethnew_handler new.h  
_y0, _y1, _ynl math.h  
_y0l, _y1l, _yn math.h  

Microsoft Foundation Classes

Digital Mars C++ for Windows and DOS includes the Microsoft Foundation Classes Version 2.5, for the Large memory model only. Digital Mars C++ for Win32 includes 32-bit MFC 3.0.

Digital Mars' versions of the Microsoft Foundation Class Library are licenced from Microsoft Corporation.

When compiling code that uses the Microsoft Foundation Classes, use the -gf option (see Compiling Code).

Memory Models

The Digital Mars C++ implementation of those 16-bit memory models also supported by Microsoft C (the Small, Medium, Compact, and Large) is similar, but not exactly the same. The significant differences are:

Huge memory model support

Digital Mars C++ does not support the Huge memory model. That is, a pointer whose type is unspecified cannot be made huge by default. However, the compiler supports huge pointers and huge data (via the __huge modifier).

Digital Mars C++ also supports the Microsoft halloc and hfree functions.

Support for based pointers

Digital Mars C++ does not support a based heap. No support for based pointers is available except for:
__based(__segname("_CODE"));
__based(__segname("_DATA")); 
__based(__segname("_STACK")); 
If your code makes use of based pointers, convert them to far pointers. Based pointers are a nonstandard construct and the code generated using them is not significantly better than for far pointers.

Assembly Language Interface

The Digital Mars C++ assembly language interface is very similar to Microsoft's. The only differences are:

Compiler Options

Digital Mars C++ provides a wide range of compiler command line options, many of which perform operations similar or identical to a Microsoft compiler option.

To convert your old Microsoft compiler command lines to the most similar Digital Mars command lines possible, use the CL utility. CL automatically converts Microsoft command lines to SC command lines, and then runs SC.


Converting from Borland

This chapter describes the differences you should consider when converting code written for Borland C++ Version 4.0 to Digital Mars C++.

Keywords

Digital Mars C++ supports many of Borland C's nonstandard keywords. The following table lists Borland's extended keywords and their Digital Mars counterparts:

Table 24-1 Support for Borland nonstandard keywords
Unsupported Borland keywords Digital Mars counterparts
_cs __cs
_ds No equivalent
_es No equivalent
_saveregs No equivalent
_seg No equivalent
_ss __ss

Predefined Macros

Digital Mars C++ supports many of Borland C's nonstandard macros. The following table lists Borland's extended macros and their Digital Mars counterparts:

Table 24-2 Support for Borland C++ nonstandard macros
Unsupported Borland macros Digital Mars counterparts comments
__BORLANDC__ __DMC__ works the same, but version numbers are for DMC
__BCPLUSPLUS__ __DMC__ works the same, but version numbers are for DMC
__CDECL__ No equivalent  
__COMPACT__ __COMPACT__  
__DLL__ _WINDLL  
__HUGE__ No equivalent  
__LARGE__ __LARGE__  
__MEDIUM__ __MEDIUM__  
__MSDOS__ No equivalent  
__PASCAL__ No equivalent  
__OVERLAY__ No equivalent  
__SMALL__ __SMALL__  
__TEMPLATES__ No equivalent  
__TINY__ __TINY__  
__TCPLUSPLUS__ __DMC__ works the same, but version numbers are for DMC
__TURBOC__ __DMC__ works the same, but version numbers are for DMC
_Windows _WINDOWS  

Header Files

The Digital Mars C++ run-time library includes all the Borland non-standard headers. Many of these headers simply reference the Digital Mars header file that contains equivalent functions. Digital Mars C++ issues a warning whenever code uses a header file. In general, we recommend switching to ANSI-compliant headers wherever possible.

Library Functions

Digital Mars C++ supports most Borland library functions. The table below lists those Borland functions that the Digital Mars C++ run-time library does not support:

Table 24-3 Unsupported Borland library functions
Unsupported functions Borland header Comments
Graphics functions graphics.h  
Text display functions conio.h  
_dos_getvect dos.h  
_dos_setvect dos.h  
_harderr dos.h  
_hardresume dos.h  
_hardreturn dos.h  
_OvrInitEms dos.h  
_OvrInitExt dos.h  
_setcursortype conio.h Use display package functions
cgets conio.h Use display package functions
cprintf conio.h Use display package functions
cputs conio.h Use display package functions
closedir dirent.h  
cscanf conio.h  
dostounix dos.h  
farheapcheck alloc.h  
farheapcheckfree alloc.h  
farheapchecknode alloc.h  
farheapfillfree alloc.h  
farheapwalk alloc.h  
getpass conio.h  
getvect dos.h  
harderr dos.h  
hardresume dos.h  
hardreturn dos.h  
heapcheck alloc.h  
heapcheckfree alloc.h  
heapchecknode alloc.h  
heapfillfree alloc.h  
heapwalk alloc.h  
import dos.h  
importb dos.h  
intr dos.h  
opendir dirent.h  
outport dos.h  
outportb dos.h  
readdir dirent.h  
rewinddir dirent.h  
setvect dos.h  
unixtodos dos.h  

Some Digital Mars C++ run-time library functions have different types or numbers of arguments from their Borland counterparts, return different values, or support different defined constants. For information on specific functions see the Runtime Library Reference.

Borland Graphics Interface

Digital Mars C++ does not support any of the functions, fonts, or drivers in the Borland Graphics Interface.

Memory Models

The Digital Mars C++ implementations of those 16-bit memory models also supported by Borland C++ (the Tiny, Small, Medium, Compact, and Large models) are similar. Their significant differences include:

Huge memory model support

Digital Mars C++ does not support the Huge memory model. That is, a pointer whose type is unspecified cannot be made huge by default. However, the compiler supports huge pointers and huge data (via the huge modifier).

Digital Mars C++ does not support the Borland halloc and hfree functions. Convert calls to these functions to the corresponding Digital Mars far calls (which have unsigned long argument types and can, therefore, allocate huge blocks) or store the affected data in a different structure (a huge array, for example).

Assembly Language Interface

The Digital Mars C++ assembly language interface is very similar to Borland's. The only differences are:

Compiler Options

Digital Mars C++ provides a wide range of compiler command line options, many of which perform operations similar or identical to a Borland C++ compiler option.

To convert Borland compiler command lines to the most similar Digital Mars command lines possible, use the BCC utility. BCC automatically converts Borland C++ command lines to SC command lines and then runs SC.

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