Qt Creator Subfolder Organization

[ChrisW67]

You are #include-ing "mainwindow.h". The first place the preprocessor will look is the compiler's current working directory which in a standard build is the folder containing the PRO file i.e. not the gui sub directory. If the file is not found there then it will search the INCLUDEPATH folders before giving up.

If you use the PRI file approach to combine files from multiple folders into a single project then often you want (or need) to set INCLUDEPATH in the sub folder PRI files:

INCLUDEPATH += gui
DEPENDPATH += gui
SOURCES += gui/mainwindow.cpp
HEADERS += gui/mainwindow.h
// Or, HEADERS += $${PWD}/mainwindow.h, see note below

INCLUDEPATH += gui
DEPENDPATH += gui
SOURCES += gui/mainwindow.cpp
HEADERS += gui/mainwindow.h
// Or, HEADERS += $${PWD}/mainwindow.h, see note below

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You can also use $${PWD} in place of a hard coded directory name so that you can rename/relocate "gui" without having to revisit the PRI files: this is not required though. DEPENDPATH is set so that Makefile rules are created to capture dependencies between files in the parent and child directories of your project.

[hiead]

Thanks for the response; however, I'm still not able to get this to work. I've changed to the following:
feather.pro

QT       += core gui
 
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 
TARGET = feather
TEMPLATE = app
 
include(gui/gui.pri)
 
SOURCES += main.cpp

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = feather
TEMPLATE = app

include(gui/gui.pri)

SOURCES += main.cpp

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gui/mainwindow.cpp

#include "gui/mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
}
 
MainWindow::~MainWindow()
{
 
}

#include "gui/mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
}

MainWindow::~MainWindow()
{

}

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gui/gui.pri

INCLUDEPATH += gui
DEPENDPATH += gui
SOURCES += gui/mainwindow.cpp
HEADERS += gui/mainwindow.h

INCLUDEPATH += gui
DEPENDPATH += gui
SOURCES += gui/mainwindow.cpp
HEADERS += gui/mainwindow.h

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(I also tried with $${PWD} in place of gui, but it did not help)

If the mainwindow class is simply in the same directory as main.cpp, it works fine; however, I do not wish to have my entire source in one directory.

[ChrisW67]

There was no need to change mainwindow.cpp, only the PRI file, and then you must rerun qmake.

//>>>>> feather.pro
 
QT       += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = feather
TEMPLATE = app
include(gui/gui.pri)
SOURCES += main.cpp
 
//>>>>> main.cpp
 
#include <QApplication>
#include "gui/mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
 
    return a.exec();
}
 
//>>>>> gui/gui.pri
 
INCLUDEPATH += gui
DEPENDPATH += gui
SOURCES += gui/mainwindow.cpp
HEADERS += gui/mainwindow.h
 
//>>>>> gui/mainwindow.h
 
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
};
 
#endif // MAINWINDOW_H
 
//>>>>> gui/mainwindow.cpp
 
#include "mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
}
 
MainWindow::~MainWindow()
{
}

//>>>>> feather.pro

QT       += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = feather
TEMPLATE = app
include(gui/gui.pri)
SOURCES += main.cpp

//>>>>> main.cpp

#include <QApplication>
#include "gui/mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

//>>>>> gui/gui.pri

INCLUDEPATH += gui
DEPENDPATH += gui
SOURCES += gui/mainwindow.cpp
HEADERS += gui/mainwindow.h

//>>>>> gui/mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
};

#endif // MAINWINDOW_H

//>>>>> gui/mainwindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
}

MainWindow::~MainWindow()
{
}

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Works fine, even if you remove the "gui/" from the #include in main.cpp.