# Structures Commands of this submenu are available in the [structures window](/8.4/user-guide/user-interface/menu-bar/view/open-subviews.md#structures-window). Only [Declare struct var...](#declare-a-structure-variable) is available in the disassembly window. * [Add struct type...](#define-a-new-structure) * [Copy struct type...](#copy-a-structure-type) * [Delete struct type...](#delete-a-structure) * [Insert gap...](#expand-a-structure) * [Delete gap...](#shrink-a-structure) * [Edit struct type...](#edit-a-structure) * [Declare struct var...](#declare-a-structure-variable) * [Force zero field offset](#force-zero-field-offset) * [Select union member...](#select-union-member) * [Create struct type from data...](#create-a-new-structure-from-current-data) * [Copy field info to pointers...](#copy-field-info-to-pointers) Use regular commands to specify struct and union members, their types, comments, etc. A union is a special kind of structure. Use structure definition commands to manipulate unions. See also [Edit](https://github.com/HexRaysSA/docs/blob/IDA-8.4/user-guide/user-interface/menu-bar/edit/edit.md) submenu. ### Define a new structure ``` Action name: AddStruct ``` This command defines a new structure or a new union. The new structure is created with zero length. You will have to add structure members using [structure](/8.4/user-guide/user-interface/menu-bar/edit/structures.md) manipulation commands. If the entered structure name denotes a standard structure type from a loaded type library, then its definition will be automatically used. In this case, the value of the 'create union' checkbox will be ignored. This command is available when you open a structures [window](/8.4/user-guide/user-interface/menu-bar/view/open-subviews.md#structures-window). You can add new members to the structure using the following commands: command hotkey ------- ------ [make data](/8.4/user-guide/user-interface/menu-bar/edit/convert-to-data.md) D [make strlit](/8.4/user-guide/user-interface/menu-bar/edit/convert-to-string-literal.md) A [make array](/8.4/user-guide/user-interface/menu-bar/edit/convert-to-array.md) \* [rename](/8.4/user-guide/user-interface/menu-bar/edit/give-name-to-the-location.md) N You may also insert/delete undefined bytes into the middle of the structure by using [expand](#expand-a-structure) and [shrink](#shrink-a-structure) commands. "Create before current structure" means that the new structure will be placed immediately before the current structure type. Otherwise, the new structure is placed after the current structure. "Don't include in the list" means that the structure will not be included in the list of the structures which appears when the user applies the structure definition, for example, when he creates a variable of this structure type. We recommend to mark this checkbox when you have defined all variables of this structure type and want to reduce the number of choices in the list. See also [How to Enter an Identifier](/8.4/user-guide/disassembler/navigation/how-to-enter-an-identifier.md). ### Copy a structure type ``` Action name: CopyStruct ``` This command makes a copy of the current structure type. The new structure type will have the same members as the current one but its name will be autogenerated (something like struc\_333) By default the new structure type will be placed after the current structure type. ### Delete a structure ``` Action name: DelStruct ``` This command deletes the current structure. Beware, when you delete a structure, all references to it will be destroyed as well. Even if you recreate it later, you'll have to specify again all references to it. You may use this command to delete unions also. This command is available when you open a structures [window](/8.4/user-guide/user-interface/menu-bar/view/open-subviews.md#structures-window). ### Expand a structure ``` Action name: ExpandStruct ``` This command expands the current structure by inserting undefined bytes at the cursor location. The cursor must not be at the end of the structure. To define a member at the end of the structure, just use normal data definition commands. This command is available when you open a structure [window](/8.4/user-guide/user-interface/menu-bar/view/open-subviews.md#structures-window). ### Shrink a structure ``` Action name: ShrinkStruct ``` This command shrinks the current structure by deleting undefined bytes at the cursor location. The cursor must be at an undefined byte. IDA will ask the user the number of bytes to remove. This command is available when you open a structure [window](/8.4/user-guide/user-interface/menu-bar/view/open-subviews.md#structures-window). ### Edit a structure ``` Action name: EditStruct ``` This command allows the user to change the structure alignment Structure alignment is used to calculate the number of padding bytes at the end of the structure. For example, if alignment is 4 and the last field is a byte at offset 11h, IDA will add 3 bytes of padding so that the struct size is 14h (multiple of 4). The alignment must be a power of 2. This command is available in the Structures [window](/8.4/user-guide/user-interface/menu-bar/view/open-subviews.md#structures-window). See also [How to Enter a Number](/8.4/user-guide/disassembler/navigation/how-to-enter-a-number.md). ### Declare a structure variable ``` Action name: MakeStructVar ``` This command declares a variable of the specified structure type. IDA will ask you to choose a structure type. You must have some structure types [defined](#define-a-new-structure) in order to use this command. If the [target assembler](/8.4/user-guide/user-interface/menu-bar/options.md#specify-target-assembler) supports it, IDA will display the structure in terse form (using just one line). To uncollapse a terse structure variable use the [Unhide](/8.4/user-guide/user-interface/menu-bar/view/unhide.md) command. You can also use this command to declare a structure field in another structure (i.e. nested structures are supported too). ### Force zero field offset ``` Action name: ZeroStructOffset ``` This command forces IDA to display a full structure member name even if the offset of the member is equal to zero. If used twice, the command cancels itself. Example: Suppose we have the following structure: ``` xxx struc a db ? b db ? c db ? xxx ends dloc xxx ? Normally IDA displays references to it like this: mov eax, offset dloc mov eax, offset dloc.b If you force IDA, then it displays member 'a': mov eax, offset dloc.a mov eax, offset dloc.b ``` ### Select union member ``` Action name: SelectUnionMember ``` This command tells IDA how to display references to a union from the current cursor location. Example: Suppose we have the following union: ``` xxx union a db ? b dw ? c dd ? ends xxx dloc xxx ? Normally, IDA displays references to "dloc" like this: mov al, byte ptr dloc mov eax, word ptr dloc After using this command, IDA can display the union members: mov al, dloc.b mov eax, dloc.d ``` ### Create a new structure from current data ``` Action name: CreateStructFromData ``` This command defines a new structure from data already defined. The new structure is created with adequate data types, and each member uses the current data name if it is available. This command is available only in the graphical version of IDA. ### Copy field info to pointers ``` Action name: CopyFieldsToPointers ``` This command scans the current struct variable and renames the locations pointed by offset expressions unless they already have a non-dummy name. It also copies the type info from the struct members to pointed locations. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.hex-rays.com/8.4/user-guide/user-interface/menu-bar/edit/structures.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. 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