Decoding IntPtr to MultiString
I need to extract environment strings from a call CreateEnvironmentBlock( out IntPtr lpEnvironment, IntPtr hToken, bool bInherit )
to put them into a dictionary based on the variable name and its value.
When this function returns, it
lpEnvironment
gets a pointer to a new environment block. The environment block is an array of nullable Unicode strings. The list ends with two zeros (\0\0
).
I can't use it easily Marshal.Copy
as I don't know the block length. I'm wondering if there is an easy way to move around it, or figure out what to copy to something that I can then convert more easily. One thought was to convey out IntPtr lpEnvironment
how out char [] lpEnvironment
.
Any suggestions?
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You don't know the full length for Marshal.Copy()
, however you know the length of the first line if you do Marshal.PtrToString()
. With this knowledge, you can move on to the next line and so on until you read a blank line, which indicates that only the \0
end of a multi-line line was present at that address .
Note that the following code assumes that Unicode is available and uses it.
[DllImport("userenv.dll", SetLastError = true, CharSet = CharSet.Unicode)]
private static extern bool CreateEnvironmentBlock(ref IntPtr lpEnvironment,IntPtr hToken,bool bInherit);
static IEnumerable<string> ExtractMultiString(IntPtr ptr)
{
while (true)
{
string str = Marshal.PtrToStringUni(ptr);
if (str.Length == 0)
break;
yield return str;
ptr = new IntPtr(ptr.ToInt64() + (str.Length + 1 /* char \0 */) * sizeof(char));
}
}
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