REGMULTISZ

REG_MULTI_SZ is a Windows Registry data type used to store multiple strings within a single value. It is one of several registry value types, alongside REG_SZ (single string) and REG_EXPAND_SZ (expandable string). REG_MULTI_SZ stores a list of strings as a sequence of Unicode strings encoded in UTF-16 little endian.

Data structure and encoding

The value data is a contiguous array of wide characters. Each string is null-terminated, and the sequence ends with an additional null terminator, creating a final empty string. In memory this appears as string1, a NUL, string2, a NUL, ..., stringN, a NUL, and a final NUL. When read, the total data length includes all characters plus the terminating nulls.

Usage and handling

Applications read and write REG_MULTI_SZ values through the Windows Registry APIs, typically RegQueryValueEx and RegSetValueEx with the type REG_MULTI_SZ. When parsing, split the data at each NUL character and stop when an empty string is encountered (the double NULL terminator). In code, the data is often handled as an array of wide strings. Tools and languages may present the value as a list of items, or require manual parsing to extract the individual strings.

Common uses

REG_MULTI_SZ is employed for settings that naturally encompass multiple items, such as a list of file extensions, search paths, or other collections of strings. It enables storing flexible, user- or application-defined lists within a single registry value.

Notes

Because the data is binary and uses UTF-16, some editors or tools may display it differently. Proper handling requires reading the raw buffer and parsing on NUL boundaries, then recognizing the final empty string as the end of the list.