尝试从matlab调用dll函数导致崩溃

Question

我正在尝试在 MATLAB 中使用第三方外部 DLL（来自 usbmicro），但它不断使 MATLAB 崩溃。这是来自说明从 C 程序中调用函数的语法的文档：

int USBm_About( char *about );

我试过这个 MATLAB 脚本（是的，它很笨拙，我是 MATLAB 菜鸟）：

>> loadlibrary('USBm.dll','USBmAPI.h')
>> libfunctions('USBm')
>> s='sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss';
>> st=strcat(s,s,s,s);
>> vp = libpointer('voidPtr',[int8(st) 0]);
>> result=calllib('USBm','USBm_About',vp)

还有这个：

>> loadlibrary('USBm.dll','USBmAPI.h')
>> libfunctions('USBm')
>> s='sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss';
>> st=strcat(s,s,s,s);
>> vp=libpointer('cstring',st);
>> result=calllib('USBm','USBm_About',vp)

在这两种情况下，calllib() 调用都会导致 MATLAB 因分段错误而崩溃。

MATLAB的版本是7.10；操作系统是 Windows Vista。

---

更新：

这是 libfunctionsview USBm 的截图：

这是头文件：

#ifndef FILE_USBmAPI_h
#define FILE_USBmAPI_h


// Prototypes for this DLL.
// These are the API functions available to the .dll user.


// Discovery routine
extern "C" __declspec(dllexport) int USBm_FindDevices(void);

// Return info about devices
extern "C" __declspec(dllexport) int USBm_NumberOfDevices(void);
extern "C" __declspec(dllexport) int USBm_DeviceValid(unsigned char);
extern "C" __declspec(dllexport) int USBm_DeviceVID(unsigned char);
extern "C" __declspec(dllexport) int USBm_DevicePID(unsigned char);
extern "C" __declspec(dllexport) int USBm_DeviceDID(unsigned char);
extern "C" __declspec(dllexport) int USBm_DeviceFirmwareVer(unsigned char);
extern "C" __declspec(dllexport) int USBm_DeviceMfr(unsigned char, char *);
extern "C" __declspec(dllexport) int USBm_DeviceProd(unsigned char, char *);
extern "C" __declspec(dllexport) int USBm_DeviceSer(unsigned char, char *);

// General USBmicro U4xx device access
extern "C" __declspec(dllexport) int USBm_ReadDevice(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_SetReadTimeout(unsigned int);
extern "C" __declspec(dllexport) int USBm_WriteDevice(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_CloseDevice(unsigned char);

// DLL string info access
extern "C" __declspec(dllexport) int USBm_RecentError(char *);
extern "C" __declspec(dllexport) int USBm_ClearRecentError(void);
extern "C" __declspec(dllexport) int USBm_DebugString(char *);
extern "C" __declspec(dllexport) int USBm_Copyright(char *);
extern "C" __declspec(dllexport) int USBm_About(char *);
extern "C" __declspec(dllexport) int USBm_Version(char *);



// General U4x1 device functions
// -----------------------------

// Port initialization
extern "C" __declspec(dllexport) int USBm_InitPorts(unsigned char);
extern "C" __declspec(dllexport) int USBm_InitPortsU401(unsigned char);
extern "C" __declspec(dllexport) int USBm_InitPortsU421(unsigned char);
extern "C" __declspec(dllexport) int USBm_InitPortsU451(unsigned char);

// Port/bit reading and writing
extern "C" __declspec(dllexport) int USBm_WriteA(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_WriteB(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_WriteABit(unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_WriteBBit(unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_ReadA(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_ReadB(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_SetBit(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_ResetBit(unsigned char, unsigned char);

// Port direction
extern "C" __declspec(dllexport) int USBm_DirectionA(unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionAOut(unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionAIn(unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionAInPullup(unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionB(unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionBOut(unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionBIn(unsigned char);
extern "C" __declspec(dllexport) int USBm_DirectionBInPullup(unsigned char);

// Strobbing a byte of data
extern "C" __declspec(dllexport) int USBm_StrobeWrite(unsigned char, unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_StrobeRead(unsigned char, unsigned char *, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_StrobeWrite2(unsigned char, unsigned char, unsigned char, unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_StrobeRead2(unsigned char, unsigned char *, unsigned char, unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_StrobeWrites(unsigned char, unsigned char *, unsigned char *);
extern "C" __declspec(dllexport) int USBm_StrobeReads(unsigned char, unsigned char *, unsigned char *);

// Reading pin-change latches
extern "C" __declspec(dllexport) int USBm_ReadLatches(unsigned char, unsigned char *);

// LCD routines
extern "C" __declspec(dllexport) int USBm_InitLCD(unsigned char, unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_LCDCmd(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_LCDData(unsigned char, unsigned char);

// SPI routines
extern "C" __declspec(dllexport) int USBm_InitSPI(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_SPIMaster(unsigned char, unsigned char *, unsigned char *);
extern "C" __declspec(dllexport) int USBm_SPISlaveWrite(unsigned char, unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_SPISlaveRead(unsigned char, unsigned char *, unsigned char *);

// 2-wire routines
extern "C" __declspec(dllexport) int USBm_Wire2Control(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_Wire2Data(unsigned char, unsigned char *);

// Stepper routine
extern "C" __declspec(dllexport) int USBm_Stepper(unsigned char, unsigned char, unsigned char, unsigned char, unsigned char, unsigned char, unsigned char, unsigned char);

// 1-wire routines
extern "C" __declspec(dllexport) int USBm_Reset1Wire(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_Write1Wire(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_Read1Wire(unsigned char, unsigned char *);
extern "C" __declspec(dllexport) int USBm_Write1WireBit(unsigned char, unsigned char);
extern "C" __declspec(dllexport) int USBm_Read1WireBit(unsigned char, unsigned char *);




#endif // multiple inclusion prevention

// End of file
//---------------------------------------------------------------------------

---

更新：

我尝试改变这一行：

extern "C" __declspec(dllexport) int USBm_About(char *);

到这里：

extern "C" __declspec(dllimport) int USBm_About(char *);

在头文件中，然后重新启动 MATLAB。我再次运行我的代码，MATLAB 仍然崩溃。

Answer 1

我从USBmicro 网站下载了DLL，并尝试通过调用loadlibrary() 来use it。不幸的是，正如你所说，这使我的 MATLAB 会话崩溃了..

在research 之后，我发现这个 DLL 公开其函数的方式与 MATLAB 期望的调用约定（cdecl 与 stdcall）不兼容。

这是我修复头文件的方法：

#ifndef FILE_USBmAPI_h
#define FILE_USBmAPI_h

#ifdef __cplusplus
extern "C" {
#endif

// ...
int __stdcall USBm_About(char *);
int __stdcall USBm_Version(char *);
// ...

#ifdef __cplusplus
}
#endif

#endif

现在您可以调用任何导出的函数。示例：

%# load library and see exported functions signatures
if ~libisloaded('USBm')
    loadlibrary('USBm.dll','USBmAPI.h')
    libfunctions('USBm','-full')
end

%# call the function: `int USBm_About(char *)`
str = repmat(' ',1,100);                           %# allocate buffer
pStr = libpointer('stringPtr',str);                %# pointer to string
[num str2] = calllib('USBm','USBm_About',pStr)
clear pStr

%# unload library
unloadlibrary USBm

注意 MATLAB 给我们的函数的签名：

[int32, cstring] USBm_About(cstring)

有趣的是，它有一个用于此函数的附加输出参数。原因是 MATLAB 并不真正支持按引用传递，尽管您可以创建与 C 指针兼容的 MATLAB 参数。

因此，如果 C 函数在通过引用传递的输入参数中返回数据，MATLAB 将创建额外的输出参数来返回这些值（以及以 Ptr 或 PtrPtr 结尾的任何输入参数）。

现在虽然输入参数pStr 类似于指向类型char 的指针，但它不是一个真正的参数，因为它不包含MATLAB 字符数组str 的地址。当函数执行时，它会返回正确的结果，但不会修改 str 中的值（在这种情况下也不会修改 pStr）。

我得到的输出是：

>> num
num =
     0

>> str2
str2 =
 USBm.dll by USBmicro L.L.C. (www.usbmicro.com). Supports: U401, U421

Answer 2

这可能是你的包含文件需要有的标准问题

extern "C" __declspec(dllexport)

当您正在构建 .dll 但 Matlab（或使用您的 .dll 的任何项目）需要：

extern "C" __declspec(dllimport)

当你包含它时。

这就是为什么人们通常有以下宏：

#ifdef USBMAPIEXPORTS 
#define USBMAPIDECLSPEC __declspec(dllexport)
#else
#define USBMAPIDECLSPEC __declspec(dllimport)
#endif

然后在标题中的函数上编写：

extern "C" USBMAPIDECLSPEC int USBm_FindDevices(void);    

并且您需要在构建 .dll 时定义 USBMAPIEXPORTS（但在 Matlab 中使用时不需要）。

请注意，这不是 Matlab 的问题。 This is the standard way to use a .dll. 你试过了吗？