The EAVCapture device needs to record its runtime log information. So for easy operation,

I choose the sqlite. It's suitable for the embedded device.

The default database file should be created automatically when the application starts at the first time.

I use the following sql statement to detect if the file is exist.

this->m_database=QsqlDatabase::addDatabase("QsqlITE");
this->m_database.setDatabaseName("EAV.db");
if(!this->m_database.open())
{
qDebug()<<"open sqlite database Failed!";
return;
}
//create table.
QsqlQuery tsqlQuery(this->m_database);
if(!tsqlQuery.exec("SELECT COUNT(*) FROM devlog"))
{
//if select is Failed,then create the table.
qDebug()<<"start to initial database";
if(!tsqlQuery.exec("CREATE TABLE devlog (CreateTime DATETIME,LogLevel INT,LogMessage BLOB)"))
{
qDebug()<<"create table failes!";
return;
}else{
qDebug()<<"create table success!";
}
}else{
qDebug()<<"database is already exists!";
}

If the file is exist,the sql statement "select count(*) from devlog" should return zero or positive value,

otherwise the exec() function will fails and return false. I can use its return value to know if it is exist.

by zhangshaoyan at May 24,2015 night.

And codes show how to insert a log message:

QString tCreateTime=QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss");
QString tsqlStatement=QString("INSERT INTO [devlog] ([CreateTime],[LogLevel],[LogMessage]) VALUES ('%1',%2,'%3')").arg(tCreateTime).arg(logLevel).arg(logMessage);
QsqlQuery tsqlQuery;
if(!tsqlQuery.exec(tsqlStatement))
{
return -1;
}
return 0;