Canon SDK-下载图像到主机

我正试图将佳能相机拍摄的图像从SD卡下载到主机上，我已经编写了代码，使其拍摄并不再保存在SD卡上，但我在主机上也找不到它。有人问路吗？？我的main和函数如下所示，不包括getFirstCamera函数。

我真的不知道回调函数等是如何工作的。。因此，如果有人能提供代码片段来修复，那就太好了

#include <stdio.h>
#include "EDSDK.h"
#include "EDSDKTypes.h"
#include "EDSDKErrors.h"
EdsError getFirstCamera(EdsCameraRef *camera);
EdsError downloadImage(EdsDirectoryItemRef directoryItem);
EdsError EDSCALLBACK handleStateEvent (EdsStateEvent event,EdsUInt32 parameter,EdsVoid * context);
EdsError EDSCALLBACK handleObjectEvent( EdsObjectEvent event,EdsBaseRef object,EdsVoid * context);
EdsError EDSCALLBACK handlePropertyEvent (EdsPropertyEvent event,EdsPropertyID property,EdsUInt32 inParam, EdsVoid * context);

int main(int argc, char **argv)
{
    EdsError err;
    EdsCameraRef camera = NULL;
    bool isSDKLoaded = false;
    EdsCapacity capacity = {0x7FFFFFFF, 0x1000, 1};
    EdsInt32 saveTarget = kEdsSaveTo_Host;
// Initialize SDK
err = EdsInitializeSDK();
if(err == EDS_ERR_OK)
{
    isSDKLoaded = true;
}
// Get first camera
if(err == EDS_ERR_OK)
{
    err = getFirstCamera (&camera);
}

// Open session with camera
    err = EdsOpenSession(camera);
// Set event handler
    if(err == EDS_ERR_OK)   err = EdsSetObjectEventHandler(camera, kEdsObjectEvent_All,handleObjectEvent, NULL);
    if(err == EDS_ERR_OK)   err = EdsSetPropertyEventHandler(camera, kEdsPropertyEvent_All,handlePropertyEvent, NULL);
    if(err == EDS_ERR_OK)   err = EdsSetCameraStateEventHandler(camera, kEdsStateEvent_All,handleStateEvent, NULL);
    err = EdsSetPropertyData( camera, kEdsPropID_SaveTo, 0, 4, &saveTarget );
    err = EdsSetCapacity(camera, capacity);
///// Take picture
    err = EdsSendCommand(camera, kEdsCameraCommand_TakePicture, 0);
////
// Close session with camera
if(err == EDS_ERR_OK)
{
    err = EdsCloseSession(camera);
}
// Release camera
if(camera != NULL)
{
    EdsRelease(camera);
}
// Terminate SDK
if(isSDKLoaded)
{
    EdsTerminateSDK();
}
}

EdsError EDSCALLBACK handleObjectEvent( EdsObjectEvent event,EdsBaseRef object,EdsVoid * context)
{
    EdsError err=EDS_ERR_OK;
switch(event)
{
    case kEdsObjectEvent_DirItemRequestTransfer:
        err = downloadImage(object);
        break;
    default:
        break;
}
// Object must be released
if(object){
    err = EdsRelease(object);
}
return err;
}
EdsError EDSCALLBACK handlePropertyEvent (EdsPropertyEvent event,EdsPropertyID     property,EdsUInt32 inParam, EdsVoid * context)
{
return EDS_ERR_OK;
}
EdsError EDSCALLBACK handleStateEvent (EdsStateEvent event,EdsUInt32 parameter,EdsVoid * context)
{
return EDS_ERR_OK;
}


EdsError downloadImage(EdsDirectoryItemRef directoryItem)
{
EdsError err = EDS_ERR_OK;
EdsStreamRef stream = NULL;
// Get directory item information
EdsDirectoryItemInfo dirItemInfo;
err = EdsGetDirectoryItemInfo(directoryItem, & dirItemInfo);
// Create file stream for transfer destination
if(err == EDS_ERR_OK)
{
err = EdsCreateFileStream(     dirItemInfo.szFileName,kEdsFileCreateDisposition_CreateAlways,kEdsAccess_ReadWrite,     &stream);
}
// Download image
if(err == EDS_ERR_OK)
{
err = EdsDownload( directoryItem, dirItemInfo.size, stream);
}
// Issue notification that download is complete
if(err == EDS_ERR_OK)
{
err = EdsDownloadComplete(directoryItem);
}
// Release stream
if( stream != NULL)
{
EdsRelease(stream);
stream = NULL;
}
return err;
}