Reading the Environment PATH Variable

The Code

The GetEnvironmentVariable() Windows API function is used to read an environment variable. The code to read the PATH variable is below. Paste the code in the CLICK event of a button in a window:

declare function GetEnvironmentVariable

VarName = "PATH"

VarLength = GetEnvironmentVariable(VarName, "", 0) + 1

VarValue = space(VarLength+1)

VarLength = GetEnvironmentVariable(VarName, VarValue, VarLength)

VarValue = VarValue[1, VarLength]

call msg(@window , 'Path is ' : VarValue)

The code is a bit tricky. Note that there are two calls to GetEnvironmentVariable(). The reason is that the PATH variable is passed as a pointer to a buffer whose size must be determined. The purpose of the first call is to determine the buffer size. The buffer size must be one byte larger than the actual value returned, because the string is terminated by a Char(0). Passing a null string in the second argument, and zero in the third argument, returns the necessary buffer size.

The second call to GetEnvironmentVariable() returns the value, including the terminating Char(0). The terminating Char(0) is stripped off. VarValue will contain the value of the PATH environment variable.

The Windows API Declaration

The code above will not run until the declaration for GetEnvironmentVariable() has been added. To add the declarations, do the following:

Log out of the application.
Log into the SYSPROG application.
Add a row, (call it DLL_APICALLS_KERNEL32), with the first line as KERNEL32 and containing the declarations as shown below.

KERNEL32
LONG STDCALL GetEnvironmentVariableA(LPCHAR, LPCHAR, ULONG) As GetEnvironmentVariable
//....add any other declarations in KERNEL32 here.....

The function is aliased to its the ANSI version GetEnvironmentVariableA().

Save the row.
Run Declare_FCNS at the System Editor Exec Line to create the declaration header, as shown below:

RUN DECLARE_FCNS 'DLL_APICALLS_KERNEL32'

Exit the editor.
Log out of SYSPROG.
Log into your application.
Run the window.