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digitalmars.D.learn - How do I convert a LPVOID (void*) to string?

reply Nieto <neto.ribeiro email.com> writes:
How do I convert/create a D string from LPVOID (void*)?


 string GetLastErrorMessage() {

	LPVOID lpMsgBuf;
	DWORD errorMessageID = GetLastError();

	FormatMessageA(
		FORMAT_MESSAGE_ALLOCATE_BUFFER |
		FORMAT_MESSAGE_FROM_SYSTEM |
		FORMAT_MESSAGE_IGNORE_INSERTS,
		NULL,
		errorMessageID,
		MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
		cast(LPSTR) &lpMsgBuf,
		0, NULL);


	return ??
}
Oct 16 2017
next sibling parent Nieto <neto.ribeiro email.com> writes:
On Monday, 16 October 2017 at 21:48:35 UTC, Nieto wrote:

 How do I convert/create a D string from LPVOID (void*)?


 string GetLastErrorMessage() {

	LPVOID lpMsgBuf;
	DWORD errorMessageID = GetLastError();

	FormatMessageA(
		FORMAT_MESSAGE_ALLOCATE_BUFFER |
		FORMAT_MESSAGE_FROM_SYSTEM |
		FORMAT_MESSAGE_IGNORE_INSERTS,
		NULL,
		errorMessageID,
		MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
		cast(LPSTR) &lpMsgBuf,
		0, NULL);


	return ??
}




I forget to call LocalFree(lpMsgBuf); here...
Oct 16 2017
prev sibling next sibling parent reply Adam D. Ruppe <destructionator gmail.com> writes:
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.
Oct 16 2017
parent Igor <stojkovic.igor gmail.com> writes:
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.
Oct 19 2017
prev sibling next sibling parent Kagamin <spam here.lot> writes:
 string GetLastErrorMessage() {

	wchar* lpMsgBuf;
	DWORD errorMessageID = GetLastError();

	uint len=FormatMessageW(
		FORMAT_MESSAGE_ALLOCATE_BUFFER |
		FORMAT_MESSAGE_FROM_SYSTEM |
		FORMAT_MESSAGE_IGNORE_INSERTS,
		NULL,
		errorMessageID,
		MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
		cast(LPWSTR) &lpMsgBuf,
		0, NULL);

	string msg=lpMsgBuf[0..len].to!string;
	LocalFree(lpMsgBuf);

	return msg;
}
Oct 19 2017
prev sibling parent reply Mike Parker <aldacron gmail.com> writes:
On Monday, 16 October 2017 at 21:48:35 UTC, Nieto wrote:

 How do I convert/create a D string from LPVOID (void*)?


 string GetLastErrorMessage() {

	LPVOID lpMsgBuf;
	DWORD errorMessageID = GetLastError();

	FormatMessageA(
		FORMAT_MESSAGE_ALLOCATE_BUFFER |
		FORMAT_MESSAGE_FROM_SYSTEM |
		FORMAT_MESSAGE_IGNORE_INSERTS,
		NULL,
		errorMessageID,
		MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
		cast(LPSTR) &lpMsgBuf,
		0, NULL);


	return ??
}




If you're using this solely for Windows error messages, the 
std.windows.syserror module has a function, sysErrorString, which 
wraps it up for you. It also provides a WindowsException you can 
throw which, given an Windows error code, will contain a 
formatted system error message.

https://dlang.org/phobos/std_windows_syserror.html
Oct 19 2017
parent Nieto <neto.ribeiro email.com> writes:
Thanks for all answers guys.


 If you're using this solely for Windows error messages, the 
 std.windows.syserror module has a function, sysErrorString, 
 which wraps it up for you. It also provides a WindowsException 
 you can throw which, given an Windows error code, will contain 
 a formatted system error message.

 https://dlang.org/phobos/std_windows_syserror.html


Yep, I was using solely for Windows error messages. In fact, I 
was trying to reinvent the wheel of wenforce(). Thanks for point 
out this. I should have asked if there was a native function for 
this rather go on and write one myself...
Oct 21 2017