Can't set cbData in RegSetValue

Question

I am trying to create a registry key with type REG_SZ and with a value longer than 4 chars.

But I can't figure out the right way to pass the data as argument :

#include <windows.h>
#include <stdio.h>


HKEY OpenKey(HKEY hRootKey, wchar_t* strKey)
{
    HKEY hKey;
    LONG nError = RegOpenKeyEx(hRootKey, strKey, 0, KEY_ALL_ACCESS, &hKey);

    if (nError == ERROR_FILE_NOT_FOUND)
    {
        printf("Debug: Creating registry key\n");
        nError = RegCreateKeyEx(hRootKey, strKey, 0, NULL, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, NULL, &hKey, NULL);
    }

    if (nError) {
        printf("Error: Could not find or create\n");
    }

    return hKey;
}

void SetValSZ(HKEY hKey, LPCTSTR lpValue, LPCTSTR data)
{
    LONG nError = RegSetValueEx(hKey, lpValue, 0, REG_SZ, (const BYTE*) data, sizeof(data));

    if (nError)
        printf("Error: Could not set registry value\n");
}

int main()
{

    HKEY hKey = OpenKey(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Policies\\Microsoft\\FVE");
    const wchar_t data[] = L"AAAABBBBCCCC";
    SetValSZ(hKey, L"RecoveryKeyMessage", data);
    RegCloseKey(hKey);

    return 0;
}

When I run it, only the first 4 characters are saved. I must have a type mistake...

Do you have any idea to help me to fix it ?

Thank you.

PS: I hope my english is clear enoth, feel free to ask me more if it isn't.

Does this answer your question? How to find the 'sizeof' (a pointer pointing to an array)? — Raymond Chen
– Raymond Chen, Commented Sep 17, 2021 at 0:25

Barmak Shemirani · Accepted Answer · 2021-09-16 23:54:45Z

1

void SetValSZ(HKEY hKey, LPCTSTR lpValue, LPCTSTR data)
{
    RegSetValueEx(hKey, lpValue, 0, REG_SZ, (const BYTE*) data, sizeof(data));
}

data is being passed as a pointer to a function, so its actual size will be lost. sizeof(data) is translated to the size of a pointer, which is 4 bytes in this case.

You have to either pass in the size as a parameter:

int len = sizeof(data);
SetValSZ(..., data, len);

Or better yet, use wcslen() to calculate the string length, then multiply that by sizeof(wchar_t).

Since you are using those T macros, the function can be written as:

RegSetValueEx(hKey,lpValue,0,REG_SZ,(const BYTE*)data,sizeof(TCHAR)*(lstrlen(data) + 1));

Edit: The size should also include the terminating null character

edited Sep 16, 2021 at 23:54

answered Sep 16, 2021 at 23:15

Barmak Shemirani

31.8k6 gold badges46 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Remy Lebeau Over a year ago

Note that when using wcslen()/lstrlen(), you have to +1 to the string length to include the null-terminator, per the documentation: "If the data is of type REG_SZ, REG_EXPAND_SZ, or REG_MULTI_SZ, cbData must include the size of the terminating null character or characters", thus you need to use sizeof(TCHAR) * (lstrlen(data) + 1) in this case.

Barmak Shemirani Over a year ago

@RemyLebeau, thanks, fixed it.

Collectives™ on Stack Overflow

Can't set cbData in RegSetValue

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related