QString::toWCharArray可以拷贝到宽字符串里

wchar_t * sourcepath=new wchar_t[MAX_PATH];

int s1=str.toWCharArray(sourcepath); 

sourcepath[s1]=0;

QString->string->wstring->LPCWSTR

QFileInfo info("./records.db");
std::string str = info.absoluteFilePath().toStdString(); //将QString转换为string
std::wstring wstr(str.length(), L' ');　　//初始化宽字节wstr
std::copy(str.begin(), str.end(), wstr.begin());　　//将str复制到wstr
LPCWSTR path = wstr.c_str();　　//将wstr转换为C字符串的指针,然后赋值给path