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c++cregistry

If Registry Key Does Not Exist

I'm adding my program to start up with:

TCHAR szPath[MAX_PATH];
GetModuleFileName(NULL,szPath,MAX_PATH);
HKEY newValue;
RegOpenKey(HKEY_CURRENT_USER,"Software\\Microsoft\\Windows\\CurrentVersion\\Run",&newValue);
RegSetValueEx(newValue,"myprogram",0,REG_SZ,(LPBYTE)szPath,sizeof(szPath));
RegCloseKey(newValue);
return 0;

And I wanted to add a check if key doesn't exists only then to create it. And something else is weird with my code I have checked the registry for my key and I see in the data column my application path + "..." (after .exe) and when I double click to check the data the popup opens and it's fine it's .exe only not .exe...

Thanks for you help :)

Solution

  • The value you wrote out is MAX_PATH bytes wide, regardless of how long the path really is. Thus you probably have a lot of non-printing characters after the .exe, and that's why you see the "...".

    The documentation says the last parameter is the size in bytes of the string, including the null terminator. So we need to know the length of the string (lstrlen(szPath)), we need to account for the null terminator (+ 1), and we need to convert from TCHARs to bytes (sizeof(TCHAR)*).

    const DWORD cbData = sizeof(TCHAR) * (lstrlen(szPath) + 1);
RegSetValueEx(newValue, "myprogram", 0, REG_SZ, (LPBYTE)szPath, cbData);

    This API is error prone, and should be used very carefully to avoid unintentional truncation or buffer overrun. (The fact that you need those casts to get it to compile should make you very cautious.) Many Windows functions that take pointers to strings want lengths in characters (which may not be bytes) or they figure out the length from the termination. This one doesn't do either of those things.