REGEXPANDSZ

REGEXPANDSZ, commonly written as REG_EXPAND_SZ, is a Windows Registry data type used to store a null-terminated Unicode string that can contain environment-variable references. Strings stored as REG_EXPAND_SZ may include placeholders like %SystemRoot% or %USERPROFILE%, allowing the value to adapt to the system or user environment.

When a value of this type is read, the registry stores the original string with the environment variables intact. To obtain the final, expanded string, applications or system components typically call an environment-variable expansion function such as ExpandEnvironmentStrings. Not all consumers automatically expand REG_EXPAND_SZ; some tools may display the raw, unexpanded string unless explicit expansion is performed.

REG_EXPAND_SZ differs from REG_SZ, which stores a plain, non-expandable string. The expandable form is useful for registry values that reference environment-dependent paths, such as file system paths or user-specific locations, enabling the same registry data to resolve differently on different systems or user accounts.

Common usage includes configuration paths or environment-sensitive values in startup scripts, system settings, and application configurations where the actual path can vary based on the system environment.

Examples of typical content include "%SystemRoot%\\System32" or "%USERPROFILE%\\Documents". After expansion, these resolve to the actual absolute paths on the machine.

See also: Windows Registry, REG_SZ, ExpandEnvironmentStrings.