Question

as far as I know strings (REG_SZ) created in the windows registry must be terminated with a 0-Byte.
But what happens if you want to create programatically a registry value with no content?

a) always terminate with 0-Byte (doesn’t matter if the registry value has content or not)

b) terminate only with 0-Byte if there is a content

Thanks!

Answer 1

You must always terminate the value with a null character. If there is no content, then the value will be that one null character and nothing else.

Note that a character is either one or two bytes long, depending on whether you are using the ANSI or Unicode APIs.

Update: The documentation for RegSetValueEx states regarding its last parameter:

The size of the information pointed to by the lpData parameter, in
bytes. 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.

The registry value types reference also says:

String Values

If data has the REG_SZ, REG_MULTI_SZ, or REG_EXPAND_SZ type, the
string may not have been stored with the proper terminating null
characters. Therefore, when reading a string from the registry, you
must ensure that the string is properly terminated before using it;
otherwise, it may overwrite a buffer. (Note that REG_MULTI_SZ strings
should have two terminating null characters.)

When writing a string to the registry, you must specify the length of
the string, including the terminating null character (\0). A common
error is to use the strlen function to determine the length of the
string, but to forget that strlen returns only the number of
characters in the string, not including the terminating null.
Therefore, the length of the string should be calculated as follows:
strlen( string ) + 1

Now all this is not as clear as it could be, but it is well known that a null terminator in Unicode strings is actually two bytes (as is every other Unicode character in the BMP).