Stores one or more numbers in binary format at the specified address+offset.

NumPut Type, Number, Type2, Number2, ... Target , Offset



Type: String

One of the following strings: UInt, UInt64, Int, Int64, Short, UShort, Char, UChar, Double, Float, Ptr or UPtr

For all integer types, or when passing pure integers, signed vs. unsigned does not affect the result due to the use of two's complement to represent signed integers.

These type names must be enclosed in quotes when used as literal strings.

For details see DllCall Types.


Type: Integer

The number to store.


Type: Object or Integer

A Buffer-like object or memory address.

Any object which implements Ptr and Size properties may be used, but this function is optimized for the native Buffer object. Passing an object with these properties ensures that the function does not write to an invalid memory location; doing so could cause crashes or other unpredictable behaviour.


Type: Integer

An offset - in bytes - which is added to Target to determine the target address. If omitted, it defaults to 0.

Return Value

Type: Integer

This function returns the address to the right of the last item written. This can be used when writing a non-contiguous sequence of numbers, such as in a structure for use with DllCall, where some fields are not being set. However, in many cases it is simpler and more efficient to specify multiple Type, Number pairs instead. Passing the address back to NumPut is less safe than passing a Buffer-like object with an updated Offset.

General Remarks

A sequence of numbers can be written by repeating Type and Number any number of times after the first Number. Each number is written at the next byte after the previous number, with no padding. When creating a structure for use with DllCall, be aware that some fields may need explicit padding added due to data alignment requirements.

If an integer is too large to fit in the specified Type, its most significant bytes are ignored; e.g. NumPut("Char", 257, buf) would store the number 1.

An exception may be thrown if the target address is invalid. However, some invalid addresses cannot be detected as such and may cause unpredictable behaviour. Passing a Buffer object instead of an address ensures that the target address can always be validated.

NumGet, DllCall, Buffer object, VarSetStrCapacity