The error of QT connecting SQLite database and its modification

In use today qt Operating the database . Because it's the first time , therefore , I met some pits , Make a note of .
System ：macOS
Language ：QT 5.12

error 1： No driver found
Error message ：QSqlError("", "Driver not loaded", "Driver not loaded")
reason
When writing the code to operate the database , First, you need a database connection , as follows ：
QSqlDatabase::addDatabase("QSQLITE");
here , The default database connection name is "qt_sql_default_connection".
If the configuration of the project is not adjusted , The executable program cannot find the database driver .
terms of settlement
open qt Project configuration , Add the path configuration of the driver to the environment variable . My configuration information is as follows ：
QT_PLUGIN_PATH=/Users/huGuohua/Qt5.12.0/5.12.0/clang_64/plugins
among , Subdirectories of the above directory sqldrivers There are various database connection drivers .

problem 2： Unable to open database
Error message ：QSqlQuery::exec: database not open
reason
Defining a QSqlQuery Variable time , A parameter is required , This parameter is used to specify the corresponding dml Which database to use . If there are no parameters when defining , The program does not prompt errors , But this dml It is not associated with database connection alone . The above error will appear .
terms of settlement
In defining dml When , It needs to be immediately associated with the corresponding database connection . That is to say ：
QSqlQuery sql_update(database);

error 3： The number of parameter bindings does not match
Error message ：QSqlError("", "Parameter count mismatch", "")
reason
The following is a process that will not make mistakes , If you don't follow this process , May cause the above errors .
When parameter binding is normally required , The code flow is ： Definition QSqlQuery, Then best clear() once , Then use prepare() To deal with the corresponding SQL.SQL There are two ways to write parameters in ：a） Question marks as placeholders ： At this point, use addBindValue To bind variables one by one ;b） The colon + Name as placeholder ： At this point, use bindValue(":name",value) To bind variables ; And then call exec To execute .exec There are many ways to write it , When binding parameters ,exec() Don't write SQL The statement itself , This is the key . If exec() contains SQL In words , Even if the above process is correct , No matter how well the parameters are bound , It's no use ,exec It directly uses SQL 了 .