objective-c - 从 cocoa 项目中的不兼容类型 "MyPrivateData *"错误分配给 'void *'

Question

我正在尝试实现 USBPrivateDataSample在我的 cocoa 项目中。问题是当我尝试为 MyPrivateData 结构分配内存时出现错误

"Assining to "MyPrivateData *" from incombatible type 'void *'"

我的头文件中有结构定义:

#define kMyVendorID     0x0403
#define kMyProductID    0x6001

class RtMidiOut;

typedef struct MyPrivateData {
    io_object_t             notification;
    IOUSBDeviceInterface    **deviceInterface;
    CFStringRef             deviceName;
    UInt32                  locationID;
} MyPrivateData;

static IONotificationPortRef    gNotifyPort;
static io_iterator_t            gAddedIter;
static CFRunLoopRef             gRunLoop;


@interface serialInput : NSObject{

...

我正在调用我的 .mm 文件:

void DeviceAdded(void *refCon, io_iterator_t iterator){
    kern_return_t       kr;
    io_service_t        usbDevice;
    IOCFPlugInInterface **plugInInterface = NULL;
    SInt32              score;
    HRESULT             res;

    while ((usbDevice = IOIteratorNext(iterator))) {
        io_name_t       deviceName;
        CFStringRef     deviceNameAsCFString;   
        MyPrivateData   *privateDataRef;
        UInt32          locationID;

        printf("Device added.\n");

        // Add some app-specific information about this device.
        // Create a buffer to hold the data.

        privateDataRef = malloc(sizeof(MyPrivateData));  //The error!

        bzero(privateDataRef, sizeof(MyPrivateData));

有什么有用的建议吗？

Answer 1

后缀mm 表示您正在使用C++ 代码和Objective-C 代码。尽管 Objective-C 是 op C 的超集，但编译器会允许它。但是你必须记住 C++ 不是 C 的超集。同样的规则不适用。

虽然 C 允许您从void * 到其他数据类型，C++ 要求您进行显式转换。

例如:

char *a;
void *b;

a = b; // allowed in C, not in C++
a = (char *)b; // allowed in C, required in C++