WvO> There are several API calls available that seem to do 
 WvO> the same thing as standard ANSI C functions, like 
 WvO> open() vs. DosOpen(), mkdir() vs. DosCreateDir() and 
 WvO> a whole bunch more that are related to file I/O.
 WvO> Is there any difference in code efficiency, EXE size 
 WvO> and speed when the OS/2 API calls are used?

The C functions will eventually call the OS/2 API's you have shown.  So
calling the OS/2 api is more direct,  but not necessarily faster.

Some thoughts:

    - The C calls are more standard (open() is POSIX, fopen() is ANSI,
      for example), so your code will work with DOS, OS/2 16, OS/2 32,
      PowerOS/2, etc without any changes.

    - Once you use printf() (or cout <<),  you have pretty much sucked
      in the whole stream library anyway,  so using DosOpen/DosRead, for
      example, to make the EXE size small won't work,  unless you avoid
      using all CRT functions.

    - Some CRT functions,  because they do some sort of local buffering,
      are faster (sometimes MUCH faster) than calling the direct OS/2
      api.  malloc() and fread()/fgets() come to mind.  fread/fwrite can
      be slower (it depends what you are doing),  but are many times
      faster -- and they are never very much slower even in the wort
      case, so I just use them.

    - The CRT functions are generally easier to use (they take fewer
      arguments),  more familiar to programmers,  and are, therefore,
      less error prone.

    - All of the C runtimes I've seen so far must have "INITINSTANCE"
      and "DATA MULTIPLE" in a *.DEF file when creating a DLL;   if you
      have advanced needs that require a "global dll",  you can not use
      *any* c runtime functions (except real simple ones like strcpy),
      so you will have to use the direct OS/2 api's.  It is not often
      an application will have to create such a DLL.

    - The code backing any OS/2 api is most likely written in C;  so
      being a hard-core pure MASM os/2 programmer may be fruitless.


 WvO> Take mkdir() as an example. I don't need to set EA's when creating a 
 WvO> particular directory, so I could be using both 
 WvO> mkdir() and DosCreateDir().

My rule:  If the CRT function will work, I use it.  I only drop down to the
OS/2 api if I need to do something special (like allocating shared memory, 
which malloc() won't do).

I don't know what compiler you're using,  but IBM Cset++ has a "tiny
runtime" option (the /Rn switch) that works well for simple programs,
if it is EXE size you are worried about.

 WvO> And the code doesn't have to be portable to other 
 WvO> operating systems.

So you say now...:-).

--- Maximus/2 2.02p1