GUI: Print command line help with -h and --help.

gui/main.cpp

@@ -21,12 +21,21 @@
 #include <QTextCodec>
 #include <QTranslator>
 #include <QMetaType>
+#include <QStringList>
+#include <iostream>
 #include "mainwindow.h"
 #include "erroritem.h"
 
+void ShowUsage();
+bool CheckArgs(const QStringList &args);
+
 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
+
+    if (!CheckArgs(app.arguments()))
+        return 0;
+
     app.setWindowIcon(QIcon(":icon.png"));
 
     // Register this metatype that is used to transfer error info
@@ -40,3 +49,25 @@ int main(int argc, char *argv[])
     window.show();
     return app.exec();
 }
+
+// Check only arguments needing action before GUI is shown.
+// Rest of the arguments are handled in MainWindow::HandleCLIParams()
+bool CheckArgs(const QStringList &args)
+{
+    if (args.contains("-h") || args.contains("--help"))
+    {
+        ShowUsage();
+        return false;
+    }
+    return true;
+}
+
+void ShowUsage()
+{
+    std::cout << "Cppcheck GUI.\n\n";
+    std::cout << "Syntax:\n";
+    std::cout << "    cppcheck-gui [OPTIONS] [files or paths]\n\n";
+    std::cout << "Options:\n";
+    std::cout << "    -h, --help    Print this help\n";
+    std::cout << "    -p <file>     Open given project file and start checking it\n";
+}