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RegSetValueEx info  Overview  Group

The RegSetValueEx function stores data in the value field of an open registry key. It can also set additional value and type information for the specified key.

LONG RegSetValueEx(

    HKEY hKey,

// handle of key to set value for

    LPCTSTR lpValueName,

// address of value to set

    DWORD Reserved,

// reserved

    DWORD dwType,

// flag for value type

    CONST BYTE *lpData,

// address of value data

    DWORD cbData 

// size of value data



Identifies a currently open key or any of the following predefined reserved handle values:

Windows NT only:
Windows 95 only: HKEY_DYN_DATA 

Points to a string containing the name of the value to set. If a value with this name is not already present in the key, the function adds it to the key.

If this parameter is NULL or points to an empty string and the dwType parameter is the REG_SZ type, this function sets the same value the RegSetValue function would set.

Reserved; must be zero.
Specifies the type of information to be stored as the value’s data. This parameter can be one of the following values:




Binary data in any form.


A 32-bit number.


A 32-bit number in little-endian format. This is equivalent to REG_DWORD.

In little-endian format, a multi-byte value is stored in memory from the lowest byte (the “little end”) to the highest byte. For example, the value 0x12345678 is stored as (0x78 0x56 0x34 0x12) in little-endian format.

Windows NT and Windows 95 are designed to run on little-endian computer architectures. A user may connect to computers that have big-endian architectures, such as some UNIX systems.


A 32-bit number in big-endian format.

In big-endian format, a multi-byte value is stored in memory from the highest byte (the “big end”) to the lowest byte. For example, the value 0x12345678 is stored as (0x12 0x34 0x56 0x78) in big-endian format.


A null-terminated string that contains unexpanded references to environment variables (for example, “%PATH%”). It will be a Unicode or ANSI string depending on whether you use the Unicode or ANSI functions.


A Unicode symbolic link.


An array of null-terminated strings, terminated by two null characters.


No defined value type.


A device-driver resource list.


A null-terminated string. It will be a Unicode or ANSI string depending on whether you use the Unicode or ANSI functions.

Points to a buffer containing the data to be stored with the specified value name.
Specifies the size, in bytes, of the information pointed to by the lpData parameter. 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.

Return Values

If the function succeeds, the return value is ERROR_SUCCESS.

If the function fails, the return value is a nonzero error code defined in WINERROR.H. You can use the FormatMessage function with the FORMAT_MESSAGE_FROM_SYSTEM flag to get a generic description of the error.


Value lengths are limited by available memory. Long values (more than 2048 bytes) should be stored as files with the filenames stored in the registry. This helps the registry perform efficiently. Application elements such as icons, bitmaps, and executable files should be stored as files and not be placed in the registry.

The key identified by the hKey parameter must have been opened with KEY_SET_VALUE access. To open the key, use the RegCreateKeyEx or RegOpenKeyEx function.

If dwType is the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type and the ANSI version of this function is used (either by explicitly calling RegSetValueExA or by not defining UNICODE before including the WINDOWS.H file), the data pointed to by the lpData parameter must be an ANSI character string. The string is converted to Unicode before it is stored in the registry.

See Also

RegCreateKeyEx, RegFlushKey, RegOpenKeyEx, RegQueryValue, RegQueryValueEx, RegSetValue

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