cannot convert ‘cv::Mat’ to ‘CvArr*

I defined the following function, but encountered a problem type conversion, the picture input for Mat type, but I want to cvPutText function realistic characters in the picture, enter the picture types require this function is CvArr * type, looking on the Internet . this approach has transformed the look of
the previous error code:

void show_dep(Mat a, int dep, int r, int c)
{
	CvFont font;
	cvInitFont(&font, CV_FONT_HERSHEY_PLAIN, 1.5f, 1.5f, 0, 2, CV_AA);
	CvPoint P1;
	P1.x=20;
	P1.y=20;
    char* depth=(char*)('0'+dep);
    const char* depth2=depth;
	cvPutText(a,depth2, P1, &font, CV_RGB(255, 0, 0));
}

Following is the correct code following improvements:
middle added two lines marked out.

void show_dep(Mat a, int dep, int r, int c)
{
	CvFont font;
	cvInitFont(&font, CV_FONT_HERSHEY_PLAIN, 1.5f, 1.5f, 0, 2, CV_AA);
	CvPoint P1;
	P1.x=20;
	P1.y=20;
    char* depth=(char*)('0'+dep);
    const char* depth2=depth;
    IplImage tmp=IplImage(a);//添加的代码
    CvArr* arr = (CvArr*)&tmp;//添加的代码
	cvPutText(arr,depth2, P1, &font, CV_RGB(255, 0, 0));