Re: How do I convert a LPVOID (void*) to string?

[Igor via Digitalmars-d-learn]

On Monday, 16 October 2017 at 22:54:32 UTC, Adam D. Ruppe wrote:
On Monday, 16 October 2017 at 21:48:35 UTC, Nieto wrote:
How do I convert/create a D string from LPVOID (void*)?

There is no one answer to this, but for the specific function 
are are looking at, the ALLOCATE_BUFFER argument means it puts 
the pointer in the pointer.

So the way I'd do it is:

char* lpMsgBuf;

instead of LPVOID. You might as well keep some type info there; 
no need to call it VOID yet (it will implicitly cast to that 
when it is necessary).

You still need to cast at the function call point, so the rest 
remains the same, but you should keep the return value of 
FormatMessageA.

Then, you can do something like this:

string s = lpMsgBuf[0 .. returned_value].idup;

and it will copy it into the D string.


You could also skip that ALLOCATE_BUFFER argument and pass it a 
buffer yourself, soemthing like:


char[400] buffer;

auto ret = FormatMessageA(
                FORMAT_MESSAGE_FROM_SYSTEM |
                FORMAT_MESSAGE_IGNORE_INSERTS,
                NULL,
                errorMessageID,
                MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                buffer.ptr,
                buffer.length, NULL);

return buffer[0 .. ret].idup;


would also work.

If you will not use this buffer in any other way but as an 
immutable string slightly better way is to:

import std.exception : assumeUnique;
return assumeUnique(buffer[0..ret]);

This will not allocate another buffer only to copy data to it as 
immutable.