--- a/src/main.cpp	Mon Jul 10 13:56:04 2017 +0300
+++ b/src/main.cpp	Wed Aug 23 13:22:27 2017 +0300
@@ -23,12 +23,30 @@
 
 
 //
+// Error logging
+//
+void slLog(QString msg)
+{
+    QString filename = qApp->applicationDirPath() + QDir::separator() + APP_LOG_FILE;
+    QFile fh(filename);
+    if (fh.open(QIODevice::WriteOnly | QIODevice::Append))
+    {
+        QTextStream out(&fh);
+        out << msg << "\n";
+        fh.close();
+    }
+}
+
+
+//
 // Display an error dialog with given title and message
 //
 int slErrorMsg(QString title, QString msg)
 {
     QMessageBox dlg;
 
+    slLog("ERROR: "+ msg);
+
     dlg.setText(title);
     dlg.setInformativeText(msg);
     dlg.setTextFormat(Qt::RichText);
@@ -95,23 +113,28 @@
 // report it to stdout if so. Return "false" if error has occured,
 // true otherwise.
 //
-bool slCheckAndReportSQLError(const QString where, const QSqlError &err)
+bool slCheckAndReportSQLError(const QString where, const QSqlError &err, bool report = false)
 {
     if (err.isValid())
     {
-        printf("SQL Error in %s: %s\n",
-            where.toUtf8().constData(),
-            err.text().toUtf8().constData());
+        slLog(
+            QStringLiteral("SQL ERROR %1: %2").
+            arg(where).arg(err.text()));
         return false;
     }
     else
+    {
+        if (report)
+            slLog(QStringLiteral("SQL OK %1").arg(where));
         return true;
+    }
 }
 
 
 void PersonInfo::dump()
 {
-    printf("PersonInfo() #%lld '%s %s' (added=%s, updated=%s, balance %1.2f)\n#%s#\n",
+    printf(
+        "PersonInfo() #%lld '%s %s' (added=%s, updated=%s, balance %1.2f)\n#%s#\n",
         id,
         firstName.toUtf8().constData(),
         lastName.toUtf8().constData(),
@@ -230,7 +253,7 @@
             arg(SQL_LEN_LAST_NAME).
             arg(SQL_LEN_EXTRA_INFO));
 
-        slCheckAndReportSQLError("CREATE TABLE people", query.lastError());
+        slCheckAndReportSQLError("CREATE TABLE people", query.lastError(), true);
     }
 
     if (!db.tables().contains("transactions"))
@@ -242,9 +265,11 @@
             "value REAL, "
             "added DATETIME NOT NULL)"));
 
-        slCheckAndReportSQLError("CREATE TABLE transactions", query.lastError());
+        slCheckAndReportSQLError("CREATE TABLE transactions", query.lastError(), true);
     }
 
+    query.finish();
+
     SyntilistaMainWindow swin;
     swin.show();
     return sapp.exec();
@@ -365,6 +390,7 @@
 //
 void SyntilistaMainWindow::statusMsg(const QString &msg)
 {
+    slLog(msg);
     ui->statusbar->showMessage(msg);
 }
 
@@ -883,7 +909,6 @@
         "(SELECT TOTAL(value) FROM transactions WHERE transactions.person=people.id) AS balance,"
         "updated FROM people";
 
-    QSqlQuery query;
     QString queryOrderDir, queryOrderBy;
 
     // Sort order
@@ -913,6 +938,7 @@
     }
 
     // Are we filtering or not?
+    QSqlQuery query;
     if (peopleFilter != "")
     {
         // Filter by name(s)
@@ -969,7 +995,7 @@
     query.addBindValue(value);
     query.addBindValue(QDateTime::currentDateTimeUtc());
     query.exec();
-    if (!slCheckAndReportSQLError("addTransaction()", query.lastError()))
+    if (!slCheckAndReportSQLError(QStringLiteral("addTransaction(%1, %2)").arg(id).arg(value), query.lastError(), true))
     {
         QSqlDatabase::database().rollback();
         return -2;
@@ -979,7 +1005,7 @@
     query.addBindValue(QDateTime::currentDateTimeUtc());
     query.addBindValue(id);
     query.exec();
-    if (!slCheckAndReportSQLError("addTransaction update timestamp", query.lastError()))
+    if (!slCheckAndReportSQLError("addTransaction update timestamp", query.lastError(), true))
     {
         QSqlDatabase::database().rollback();
         return -3;
@@ -1351,7 +1377,6 @@
         return -1;
 
     QSqlDatabase::database().commit();
-
     updateModel();
     return 0;
 }

--- a/src/main.h	Mon Jul 10 13:56:04 2017 +0300
+++ b/src/main.h	Wed Aug 23 13:22:27 2017 +0300
@@ -25,7 +25,7 @@
 #define APP_ID            "Kampus Syntilista"       // Application ID (for settings)
 #define APP_NAME          "Café Kampus Syntilista"  // Application title/name
 #define APP_SQLITE_FILE   "syntilista.sqlite3"      // SQLite3 database file name (without path)
-
+#define APP_LOG_FILE      "log.txt"                 // Application log file
 
 #define SQL_LEN_FIRST_NAME 128
 #define SQL_LEN_LAST_NAME  128