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   <TITLE>Get the location of the Windows directory or the Windows system directory</TITLE>

   <META NAME="Author" CONTENT="Harold Howe">

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<H3>

Get the location of the Windows directory or the Windows system directory

</H3>

<P>

 Call the API <TT>GetWindowsDirectory</TT> function to get the windows

directory. Call <TT>GetSystemDirectory</TT> if you want to find the windows system

directory.

</P>

<pre>

<font color="navy">// Fetch the windows directory</font>

<b>char</b> WinDir<b>[</b>MAX_PATH <b>+</b><font color="blue">1</font><b>]</b><b>;</b>

WinDir<b>[</b>MAX_PATH<b>]</b> <b>=</b> <font color="blue">'\0'</font><b>;</b>

GetWindowsDirectory<b>(</b>WinDir<b>,</b>MAX_PATH<b>)</b><b>;</b>



<font color="navy">// fetch the system directory</font>

<b>char</b> SysDir<b>[</b>MAX_PATH <b>+</b><font color="blue">1</font><b>]</b><b>;</b>

SysDir<b>[</b>MAX_PATH<b>]</b> <b>=</b> <font color="blue">'\0'</font><b>;</b>

GetSystemDirectory<b>(</b>SysDir<b>,</b> MAX_PATH<b>)</b><b>;</b>

</pre>

<P>

<B>Note:</B> The windows directory is usually <TT>C:\WINDOWS</TT> or <TT>C:\WINNT</tt>.

The system directory is usually <TT>C:\WINDOWS\SYSTEM32</tt> or <TT>C:\WINNT\SYSTEM32</tt>.

</P>

<P>

<B>Note:</B> The second argument to both <tt>GetWindowsDirectory</tt> and

<TT>GetSystemDirectory</tt> specifies how many characters the OS can copy into

the string's buffer. If this argument is less than the number of characters

needed for the directory name, then both functions will return the size of the

buffer required to hold the entire string (including the null terminator).

No data is copied when the buffer size is too small.

</P>

<P>

Some people employ a technique that takes advantage of this fact. The technique

works like this. You call <tt>GetWindowsDirectory</tt> twice. The first time you

call it, you pass a <TT>NULL</TT> pointer, and 0 for the number of bytes that

can be written. The API will return how many bytes you need to allocate for the

string buffer. Using this information, you can call <TT>new</TT> to create a

string that is exactly the correct size. Here is how it works:

</P>

<pre>

UINT len <b>=</b> GetWindowsDirectory<b>(</b>NULL<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>  <font color="navy">// fetch size</font>

<b>char</b> <b>*</b>buf <b>=</b> <b>new</b> <b>char</b><b>[</b>len<b>]</b><b>;</b>                <font color="navy">// allocate buffer</font>

GetWindowsDirectory<b>(</b>buf<b>,</b> len<b>)</b><b>;</b>            <font color="navy">// call API again</font>

<b>...</b>

<b>delete</b> <b>[</b><b>]</b>buf<b>;</b>                             <font color="navy">// cleanup</font>

</pre>

<P>

Usually, it is easier to just use an array with a size of <TT>MAX_PATH</TT>.

However, this technique of calling an API function twice, once to calculate a

buffer size, and once to actually fetch the string, appears in other

situations where a constant such as MAX_PATH is not available.

</P>

<P>

<B>Note:</B> The documentation states that the buffer passed to

<tt>GetWindowsDirectory</tt> and <TT>GetSystemDirectory</tt> should be at least

<TT>MAX_PATH</TT> bytes in length to guarantee the that string will fit. Now does the

documentation mean that the buffer should be able to hold a string with

a length of <tt>MAX_PATH</tt> characters? If so, then the buffer should be

<tt>MAX_PATH+1</TT> bytes long, to accomodate the null terminator. Or does the

documentation mean that the buffer should be <TT>MAX_PATH</TT> bytes long,

because the largest possible string returned will be <TT>MAX_PATH-1</TT>

characters long?

</P>

<P>

I don't know the correct answer, so I usually error on the side of caution.

I make the buffer <tt>MAX_PATH+1</tt> bytes long, in case the directory has a

string length of <TT>MAX_PATH</TT>. <tt>MAX_PATH</tt> is defined as 260 in

<TT>windefs.h</TT>.

</P>

<P>

<B>Note:</B> The string returned by <tt>GetWindowsDirectory</tt> does not contain

a trailing slash. The return string will be <TT>C:\WINDOWS</TT> and not <TT>C:\WINDOWS\</TT>.

<TT>GetSystemDirectory</tt> works the same way.

</P>

<P>

Be aware that not all of the directory based API fucntions work the same way. For

example, <TT>GetTempPath</TT> does include a trailing slash. 



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