3.6. Structures, Records

3.6.1. Simple Structures

C structures are similar to records in Delphi. Structures are usually defined with the typedef keyWord, but it's also possible to do it with #define.

The format of a structure declaration is

{Struct|Union} [OptIdentifier] [TagName]
{ FieldDefinitions [; ...]}
[Name [...]]

You can ignore the TagName. It's used in C for subsequent references to the structure.

This is how the fields within a structure are defined:

#define RASENTRYNAMEA struct tagRASENTRYNAMEARASENTRYNAMEA{    DWORD dwSize;    CHAR  szEntryName[ RAS_MaxEntryName + 1 ];};

This C declaration defines a record (structure) named RASENTRYNAMEA. The Delphi-style name would be TRASENTRYNAMEA. This structure contains two fields: the first is named dwSize and has the type DWord. The second field is an array of char with RAS_MaxEntryName + 1 elements.

The Delphi translation:

TYPE  PRASEntryName = ^TRASEntryName  TRASEntryName = Record    dwSize : DWORD;    szEntryName : Array [0..RAS_MaxEntryName] of Char  end

Remember, you may not declare the array of char with a range from 0 to RAS_MaxEntryName+1. The reason is, that in C the number of elements is specified, but in Delphi the range of elements. Read more in the chapters about Arrays and Strings.

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3.6.2 Unions in Structures

C unions in structures are comparable to variant parts of records in Delphi. Blocks declared in a union structure are not consecutive but overlaid.

typedef struct _PROCESS_HEAP_ENTRY {    PVOID lpData;    DWORD cbData;    BYTE cbOverhead;    BYTE iRegionIndex;    WORD wFlags;    union {        struct {            HANDLE hMem;            DWORD dwReserved[ 3 ];        } Block;        struct {            DWORD dwCommittedSize;            DWORD dwUnCommittedSize;            LPVOID lpFirstBlock;            LPVOID lpLastBlock;        } Region;    };} PROCESS_HEAP_ENTRY, *LPPROCESS_HEAP_ENTRY, *PPROCESS_HEAP_ENTRY;

This is the translation into Delphi:

type  PProcessHeapEntry = ^TProcessHeapEntry;  TProcessHeapEntry = Record    lpData: Pointer;    cbData: DWord;    cbOverhead: Byte;    iRegionIndex: Byte;    wFlags: Word;    case Integer of      0: (Block: Record            hMem: Thandle            Reserved : Array [0..2] of DWord;          end);      1: (Region: Record            dwCommittedSize: DWord;            dwUnCommittedSize: DWord;            lpFirstBlock: Pointer;            lpLastBlock: Pointer          end);  end;