zDoes zDoes - 28 days ago 7
C++ Question

How to append select query results in a QTextEdit panel?

I'm work in a project where I need to execute a select query(I use sqlite as a sql engine) and load the result into a QTextEdit(I use QT for my graphical interface).

For now I wrote only the following code(but I stuck in the part where I need to append the result to the QTextEdit):

//Callback function to print the query to the console
int db_files::CallBack(void *notUsed, int argc, char **argv, char **azColName) {
for(int i = 0; i<argc; i++) {
printf("%s : %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
}
std::cout << "\n";
return 0;
}

//Function where I open the database and run the query
void custHandler::show_all() {
rc = sqlite3_open("database.db", &db);
if(rc != SQLITE_OK) {
sqlite3_close(db);
exit(1);
}
sqlCust = "SELECT * FROM DB";
rc = sqlite3_exec(db, sqlCust, CallBack, 0, &ErrMsg);
if (rc != SQLITE_OK) {
exit(1);
}
sqlite3_free(ErrMsg);
sqlite3_close(db);
}


Maybe I need to operate in the callback function, but I don't know how ... someone can explain it to me?

EDIT:
I have a QTextEdit variable called txtShow, i usually access it by
ui->txtShow.insertPlainText("text");

Answer Source

See the synopsis of the sqlite3_exec() function in the SqlLite documentation:

int sqlite3_exec(
  sqlite3*,                                  /* An open database */
  const char *sql,                           /* SQL to be evaluated */
  int (*callback)(void*,int,char**,char**),  /* Callback function */
  void *,                                    /* 1st argument to callback */
  char **errmsg                              /* Error msg written here */
);

As you see the 4th parameter is a user defined argument that will be passed to the callback() function.

So you'll need to use that too interact with your calling code:

//Callback function to print the query to the console
int db_files::CallBack(void *myQTextEdit, int argc, char **argv, char **azColName) {
    QTextEdit* qTextEdit = (QTextEdit*)myQTextEdit;

    for(int i = 0; i<argc; i++) {
        // Add the results to qTextEdit as needed ...
    }
    return 0;
}

When calling the sqlite3_exec() function pass that:

//Function where I open the database and run the query
void custHandler::show_all() {
     rc = sqlite3_open("database.db", &db);
     if(rc != SQLITE_OK) {
          sqlite3_close(db);
          exit(1);
      }
      sqlCust = "SELECT * FROM DB";
      rc = sqlite3_exec(db, sqlCust, CallBack, &myQTextEdit, &ErrMsg);
                                            // ^^^^^^^^^^^^

      if (rc != SQLITE_OK) {
          exit(1);
      }
      sqlite3_free(ErrMsg);
      sqlite3_close(db);
}

That's a very common way how C-style API's interact with user code in callback functions.