Thread: GetLastError always returns zero

Hi All,
I tried to read a key and its value from windows registry. I succeeded in it. But i want to know the error code returned by those functions and hence made the function to fail (by asking program to get value for a non-existing key). GetLastError i used. But it always returns zero as the error code.
Can anyone help me in this regard.
Thanks in advance.

What version of Windows are you running? The 16bit cored systems, (95,98,ME), do not fully implement GetLastError() and frequently return zero even if there is an error.

Hi all,
I am using win2k os. Code is very simple. Here is this:

Code:

#include<windows.h>
#include<stdio.h>
void printerror(char*);
int main()
{
	HKEY hkey;
	//LPCTSTR lpsubkey;	
	int err,sizekeyvalue=30;
	char keyvalue[30];	
	err=RegOpenKeyEx(HKEY_LOCAL_MACHINE,"SOFTWARE\\Sarav",0,KEY_READ,&hkey);
	if(err==ERROR_SUCCESS)
	{
		printf("\nRegistry value read successfully\n");
	}
	else
	{
		printerror("RegOpenKeyEx");		
	}
	err=RegQueryValueEx(hkey,"Protocol",0,0,(LPBYTE)keyvalue,&sizekeyvalue);
	if(err==ERROR_SUCCESS)
	{
		printf("\nThe string is %s\n",keyvalue);
	}
	else
	{
		printerror("RegQueryValue");
	}
	RegCloseKey(hkey);
}
void printerror(char *msg)
{
	DWORD dwErrno;
	char errmsg[30];
	dwErrno=GetLastError();
	sprintf(errmsg,"%s Failed:Error No is %u",msg,dwErrno);
	printf("\n%s\n",errmsg);
}

Neither of the functions you are using use the GetLastError() mechanism, rather, they return the winerror.h value directly. From MSDN...

>>>
Return Values
If the function succeeds, the return value is ERROR_SUCCESS.

If the function fails, the return value is a nonzero error code defined in WINERROR.H. You can use the FormatMessage function with the FORMAT_MESSAGE_FROM_SYSTEM flag to get a generic description of the error.
<<<

... routines that require you to call GetLastError() mention it in this section of the documentation.

As an aside, it is always a good idea to call GetLastError() immeadiately after a failing call. All kinds of things can reset this value.

Thanks adrianxw,
I made variable=RegOpenKeyEx() to get fail and the error value is present in "variable" itself. Now i am able to get error value correclty.But why GetLastError() fails to give correct error value?

>>> I made variable=RegOpenKeyEx() to get fail and the error value is present in "variable" itself.

Err, you had that already, (err = )...

>>> But why GetLastError() fails to give correct error value?

... as I said...

>>> Neither of the functions you are using use the GetLastError() mechanism

Yes salem,
I found that(buffer overflow) and I corrected it already..Thanks.

Hi adrianxw,
I just mentioned "variable" in generic sense for clarity.. I used only "err".