Datatypes for external function arguments

When you declare an external function in PocketBuilder, the datatypes of the arguments must correspond with the datatypes as declared in the function’s source definition. This section documents the correspondence between datatypes in external functions and datatypes in PocketBuilder. It also includes information on byte alignment when passing structures by value.

Use the tables to find out what PocketBuilder datatype to use in an external function declaration. The PocketBuilder datatype you select depends on the datatype in the source code for the function. The first column lists datatypes in source code. The second column describes the datatype so you know exactly what it is. The third column lists the PocketBuilder datatype you should use in the external function declaration.

Boolean

BOOL on Windows is 16-bit, signed. It is declared in PocketBuilder as boolean.

Pointers

**Table 3-9: PocketBuilder datatypes for pointers**
Datatype in source code	Size	PocketBuilder datatype
* (any pointer)	32-bit pointer	Long
byte *	Array of bytes of variable length	Blob

Windows 32-bit FAR pointers, such as LPBYTE, LPDWORD, LPINT, LPLONG, LPVOID, and LPWORD, are declared in PocketBuilder as long datatypes. HANDLE is defined as 32 bits unsigned and is declared in PocketBuilder as an UnsignedLong.

Near-pointer datatypes (such as PSTR and NPSTR) are not supported in PocketBuilder.

Characters and strings

**Table 3-10: PocketBuilder datatypes for characters and strings**
Datatype in source code	Size	PocketBuilder datatype
char	16 bit Unicode	Char
string	32-bit pointer to a null-terminated array of Unicode characters of variable length	String

The Windows 32-bit FAR pointer LPSTR is declared in PocketBuilder as string.

Reference arguments When you pass a string to an external function by reference, all memory management is done in PocketBuilder. The string variable must be long enough to hold the returned value. To ensure that this is true, first declare the string variable, and then use the Space function to fill the variable with blanks equal to the maximum number of characters that you expect the function to return.

Fixed-point values

**Table 3-11: PocketBuilder datatypes for fixed-point values**
Datatype in source code	Size	PocketBuilder datatype
short	16 bits, signed	Integer
unsigned short	16 bits, unsigned	UnsignedInteger
int	32 bits, signed	Long
unsigned int	32 bits, unsigned	UnsignedLong
long	32 bits, signed	Long
unsigned long	32 bits, unsigned	UnsignedLong
longlong	64 bits, signed	LongLong

The Windows definition WORD is declared in PocketBuilder as UnsignedInteger and the Windows definition DWORD is declared as an UnsignedLong. You cannot call external functions with return values or arguments of type short.

Floating-point values

**Table 3-12: PocketBuilder datatypes for floating-point values**
Datatype in source code	Size and precision	PocketBuilder datatype
float	32 bits, single precision	Real
double	64 bits, double precision	Double

PocketBuilder does not support 80-bit doubles on Windows.

Date and time

The PocketBuilder datatypes Date, DateTime, and Time are structures and have no direct equivalent for external functions in C.

Passing structures by value

You can pass PocketBuilder structures to external C functions if they have the same definitions and alignment as the structure’s components. The DLL or shared library must be compiled using byte alignment; no padding is added to align fields within the structure.