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Chapter 4

Windows 3.1 Compiler/Linker Issues

National Instruments Corporation

4-5

LabWindows/CVI Programmer Reference Manual

•

You can use the argument types

char

unsigned char

int

unsigned int

short

unsigned short

long

unsigned long

float

, and

double

, as well as pointers to

any type, and arrays of any type. You can use typedefs for these types.

•

You can use the return types

void

char

unsigned char

int

unsigned int

short

unsigned short

long

, and

unsigned long

, as well as pointers to any type.

You can use typedefs for these types.

•

You can use the return types float and double only if the DLL is created with a
Microsoft C compiler, and the functions returning floats or double are declared with the

cdecl

calling convention. You do not have to modify the glue code generated for

functions that return float or double values.

•

In the DLL header file, enum sizes must be consistent between LabWindows/CVI and the
compiler for the DLL.

typedef enum {

No_Error,

Device_Busy,

Device_Not_Found

} ErrorType;

The size of

ErrorType

is 2 bytes in Visual C++, whereas it is 1 byte in

LabWindows/CVI. To force LabWindows/CVI to treat

ErrorType

as 2 bytes, add

another enum value explicitly initialized to a 2-byte value, such as the following.

ErrorType_Dummy = 32767

•

If the DLL you are using performs DMA on a buffer you pass to it, you might experience
a problem. The DLL might attempt to lock the buffer in memory by calling the Windows
SDK function

GlobalPageLock

fails on buffers allocated with the

Watcom

malloc

function that LabWindows/CVI uses in 32-bit mode.

Write the DLL so that if

GlobalPageLock

fails, the DLL attempts to lock the buffer

with the following code:

int DPMILock (void *buffer, unsigned long size)

{

DWORD base;

unsigned sel, offset;

union _REGS regs;

sel = SELECTOROF(buffer);

offset = OFFSETOF(buffer);

base = GetSelectorBase(sel);

base = base+offset;

regs.x.ax = 0x600; /* DPMI lock memory function */

regs.x.bx = HIWORD(base);

regs.x.cx = LOWORD(base);

regs.x.di = LOWORD(size);

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