xHarbour Reference Documentation > Function Reference

HB_SizeofCStructure()

Calculates the amount of memory required to store a C structure.

Syntax

HB_SizeofCStructure( <aTypes>, [<nAlign>] ) --> nBytes

Arguments

<aTypes>

The C-data types for each structure member must be specified as a one dimensional array of the same number of elements as there are structure members. #define constants must be used for <aTypes>. The following constants are available in the Cstruct.ch file:

Constants for C-data types

Constant	C-data type
CTYPE_CHAR	char
CTYPE_UNSIGNED_CHAR	unsigned char
CTYPE_CHAR_PTR	char *
CTYPE_UNSIGNED_CHAR_PTR	unsigned char*
CTYPE_SHORT	short
CTYPE_UNSIGNED_SHORT	unsigned short
CTYPE_SHORT_PTR	short *
CTYPE_UNSIGNED_SHORT_PTR	unsigned short *
CTYPE_INT	int
CTYPE_UNSIGNED_INT	unsigned int
CTYPE_INT_PTR	int *
CTYPE_UNSIGNED_INT_PTR	unsigned int *
CTYPE_LONG	long
CTYPE_UNSIGNED_LONG	unsigned long
CTYPE_LONG_PTR	long *
CTYPE_UNSIGNED_LONG_PTR	unsigned long *
CTYPE_FLOAT	float
CTYPE_FLOAT_PTR	float *
CTYPE_DOUBLE	double
CTYPE_DOUBLE_PTR	double *
CTYPE_VOID_PTR	void *
CTYPE_STRUCTURE	struct
CTYPE_STRUCTURE_PTR	struct *

<nAlign>

Optionally, the byte alignment for C-structure members can be specified. By default, the members are aligned at an eight byte boundary. Note that Windows API functions require a four byte alignment for structures.

Return

The function returns the memory requirement for a structure as a numeric value in bytes.

Description

Function HB_SizeOfCStructure() is used to calculate the size of a C structure in bytes. This depends on the number of bytes each C data type of structure members occupies in memory, and the byte alignment. The returned value is then used to create a character string like Replicate(Chr(0), nBytes). This character string can then be passed by reference to an API function via DllCall(). When DllCall() returns, the changed C structure string is decoded with function HB_StructureToArray().

An easier way of obtaining the size of a C structure is to declare a C structure class with typedef struct and call method :sizeOf() of a C structure object.

Info

See also:	C Structure class, HB_ArrayToStructure(), HB_StructureToArray(), pragma pack()
Category:	C Structure support , xHarbour extensions
Header:	cstruct.ch
Source:	vm\arrayshb.c
LIB:	xhb.lib
DLL:	xhbdll.dll