怎么给cvOpenFileStorage绝对路径

Question

我需要将绝对路径放在cvOpenFileStorage函数中但是当我编写这段代码时，pFileStorage指针总是为NULL，我该怎么办？

CvFileStorage* pFileStorage;

    char XML_File [100];
    strcpy( XML_File , "c:\\facedata.xml");

    pFileStorage = cvOpenFileStorage(XML_File, 0, CV_STORAGE_WRITE);