C++ uninitialized local variable

Question

I have a function:

VOID GetOSVersion(PDWORD major, PDWORD minor, PDWORD build)
{
    OSVERSIONINFO osver;
    ZeroMemory(&osver, sizeof(OSVERSIONINFO));
         


        

Answer 1

the problem is there:

DWORD major;
DWORD minor;
DWORD build;
GetOSVersion(&major, &minor, &build);

Fix:

VOID GetOSVersion(PDWORD major, PDWORD minor, PDWORD build)
{
    OSVERSIONINFO osver = {};
    osver.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
    GetVersionEx(&osver);
    if(major)
    *major = osver.dwMajorVersion;
    if(minor)
    *minor = osver.dwMinorVersion;
    if(build)
    *build = osver.dwBuildNumber;
}

DWORD major = 0;
DWORD minor = 0;
DWORD build = 0;
GetOSVersion(&major, &minor, &build);

PDWORD is pointer to DWORD. All three parameters are output parameters. In C/C++, it's a common usage: if you want to return more then one value from a function, you need pass pointer (or reference too in case of c++) to a variable:

int var = 0;
if(some_function_that_can_fail_and_write_result(&var))
 ;//do something

In your case you are passing uninitialized pointer to a function by value. It's the same as:

void foo(int parameter);
// ...
int a;
foo(a);

You have a lot of ways:

Pass uninitialized pointer by reference:

VOID GetOSVersion(PDWORD& major, PDWORD&, PDWORD&)
{
//...
major = new DWORD(osver.dwMajorVersion);

}
// usage:
PDWORD major;
GetOSVersion(major, ....);

//...
delete major;

Pass all parameters by reference:

VOID GetOSVersion(DWORD& major, DWORD&, DWORD&)
{
//...
major = osver.dwMajorVersion;

}
// usage:
DWORD major = 0;
GetOSVersion(major, ....);

Use your version of GetOSVersion(), but with the fix in this answer on the beginning