Converting LPCSTR to LPVOID

[Toni]

Hello Everyone ,
I'm trying to convert an LPCSTR to LPVOID for use in DeviceIOControl.
But when i use LPVOID test = (LPVOID)test_lpcstr then it doesn't work ,
When i use LPVOID test = "TEST" , then it works , so it must have something to do with the conversion.
Any ideas ?

Note: i'm very new to C++
Sorry for my poor english

Edit: DeviceIoControl(driverHandle, CHANGE_PREFIX, "TEST", sizeof("TEST"), szTemp, sizeof(szTemp), &dwReturn, NULL) Works , but
LPVOID var = "TEST";
DeviceIoControl(driverHandle, CHANGE_PREFIX, var, sizeof(var), szTemp, sizeof(szTemp), &dwReturn, NULL);
Doesn't.

[Banfa]

Please discribe what you mean by

"it doesn't work"

[Toni]

Well....it doesn't send the string to the driver...

[Banfa]

Well....it doesn't send the string to the driver...

The problem is not the pointer but your use of the sizeof operator

sizeof("TEST") = 5 (4 characters of TEST plus the NULL terminator)

LPVOID var = "TEST";

sizeof(var) = 4 (size of a pointer)

Obviously you may expect this to work with "TEST" but not with a longer string.

You should use strlen to get the length of your input buffer string if it is actully a string.

Also why declare a LPVOID, why not just use a char * ?

[Toni]

well.... i think i did have to declare an LPVOID because of the MSDN docs...

[Toni]

Okay , i fixed it! , but it did work fine with sizeof
this was the code:
char test[256] = {"TEST"};
char szTemp[256] = {0};
DeviceIoControl(driverHandle, CHANGE_PREFIX, test, sizeof(test), szTemp, sizeof(szTemp), &dwReturn, NULL);

But now i did got another problem , i can't use this code:
LPCSTR test_str = "TEST";
char test[256] = {(char)test_str};

do you know how to do it?

[Banfa]

Okay , i fixed it! , but it did work fine with sizeof
this was the code:
char test[256] = {"TEST"};
char szTemp[256] = {0};
DeviceIoControl(driverHandle, CHANGE_PREFIX, test, sizeof(test), szTemp, sizeof(szTemp), &dwReturn, NULL);

That is because in this code you are taking sizeof an array where originally you where taking sizeof a pointer. I have seen many people accidentally declare the wrong thing because of MS docs, articularly declaring pointers where they should be declaring objects and dereferencing them.

But now i did got another problem , i can't use this code:
LPCSTR test_str = "TEST";
char test[256] = {(char)test_str};

do you know how to do it?

You can not initialise a char array from a pointer to char just use strcpy to copy the data from the pointer to the array.

strcpy(test, test_str);

[Toni]

Thanks!
I'm now developing a driver which uses these arguments....
I can use it with DbgPrint but not with memcmp...this is the code ,
PCHAR pInputBuffer = Irp->AssociatedIrp.SystemBuffer;
if(pInputBuffer) {
if(StringNullTerminated(pInputBuffer,irpStack->Parameters.DeviceIoControl.InputBufferLength,&dwD ataRead))
{
test = (const void*)pInputBuffer;
DbgPrint(test);
}
if(0 == memcmp( process_name.Buffer, test, 4)) {
DbgPrint("It worked!");
}

Note: process_name is an ANSI_STRING , test is declared as const void *test
irpStack is a PIO_STACK_LOCATION

Hope the code and the notes helps ,
Bye!
Toni

Edit: dwDataRead is declared as UINT dwDataRead = 0 and Irp is declared as IN PIRP Irp