Passing char[] reference to unmanaged environment?

[Albertas]

Hello,

I have function written in unmanaged environment, which takes as
parameters char*. For example:
void function(char *input, char *output);
It takes two char arrays and modifies the output char array. Now when i

try to use it in managed environment, i do this:


[DllImport("dll.dll", EntryPoint="function",
ExactSpelling=false, SetLastError=true)]
public unsafe static extern void
function([MarshalAs(UnmanagedType.LPArray)] char[] input,
[MarshalAs(UnmanagedType.LPArray)] ref char[] output);


Also tried byte[] instead of char.


When i call it i use:


function (input, ref output);


The problem is when i call this function, the output char array has
only one member in it, but there should be more. What I'm doing
wrong?


The function dll is not a COM object.


Thank You

 

[Ben Voigt]

Hello,

I have function written in unmanaged environment, which takes as
parameters char*. For example:
void function(char *input, char *output);
It takes two char arrays and modifies the output char array. Now when i

try to use it in managed environment, i do this:


[DllImport("dll.dll", EntryPoint="function",
ExactSpelling=false, SetLastError=true)]
public unsafe static extern void
function([MarshalAs(UnmanagedType.LPArray)] char[] input,
[MarshalAs(UnmanagedType.LPArray)] ref char[] output);


Also tried byte[] instead of char.


When i call it i use:


function (input, ref output);


The problem is when i call this function, the output char array has
only one member in it, but there should be more. What I'm doing
wrong?

Since the unmanaged code isn't aware of .NET memory allocation, it can't
resize the output array. You should therefore allocate the output array
before the call. There should also be no need to use "ref" on the output
array, as the function modifies the existing array.