MySql error: SqlError(Unable to execute query", "Can't create/write to file OS errno 2 - No such file...

Question:

When I tried to use the command to write the data in mysql to the database today, I reported an error:

QSqlError("1", "QMYSQL: Unable to execute query", "Can't create/write to file 'd:\test.xls' (OS errno 2 - No such file or directory)")

My command is this:

QString strFileName = QString("select * from result where ") + str + "into outfile 'd:\\test.xls'";

I found a lot of solutions on the Internet:

Big Brother 1
Big Brother 2

Try if you can solve your problem, if not, try it

My:

QString strFileName = QString("select * from result where ") + str + "into outfile 'd:/test.xls'";

In database writing, try to use less backslashes and more slashes.I think my error is because of this.I still don't use backslashes anymore.
Of course, my approach may only be adapted to my problem.If you can't solve your problem, please don't spray me, thank you guys.
I am just an ordinary code farmer in the code field~