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When I tried compiling a program;

/*
 * Copyright (c) 2006-2007, Johan Thelin
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, 
 * are permitted provided that the following conditions are met:
 * 
 *     * Redistributions of source code must retain the above copyright notice, 
 *       this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright notice,  
 *       this list of conditions and the following disclaimer in the documentation 
 *       and/or other materials provided with the distribution.
 *     * Neither the name of APress nor the names of its contributors 
 *       may be used to endorse or promote products derived from this software 
 *       without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
 
#include <QList>
#include <QString>

#include <QtDebug>

void fillAndPrint()
{
  QList<QString> list;
  list << "foo" << "bar" << "baz";

  QString s;
  foreach( s, list )
    qDebug() << s;
}

void constIterators()
{
  QList<int> list;
  list << 23 << 27 << 52 << 52;
  
  QListIterator<int> javaIter( list );
  while( javaIter.hasNext() )
    qDebug() << javaIter.next();
    
  QList<int>::const_iterator stlIter;
  for( stlIter = list.begin(); stlIter != list.end(); ++stlIter )
    qDebug() << (*stlIter);
}

void mutableIterators()
{
  QList<int> list;
  list << 27 << 33 << 61 << 62;
  
  QMutableListIterator<int> javaIter( list );
  while( javaIter.hasNext() )
  {
    int value = javaIter.next() + 1;
    javaIter.setValue( value );
    qDebug() << value;
  }
  
  QList<int>::Iterator stlIter;
  for( stlIter = list.begin(); stlIter != list.end(); ++stlIter )
  {
    (*stlIter) = (*stlIter)*2;
    qDebug() << (*stlIter);
  }
}

void insertAndPrint()
{
  QList<QString> list;

  list << "first";
  list.append( "second" );
  list.prepend( "third" );
  list.insert( 1, "fourth" );
  list.insert( 4, "fifth" );
  
  QString s;
  foreach( s, list )
    qDebug() << s;
}

void miscExamples()
{
  QList<int> list;
  for( int i=0; i<10; i++ )
    list << i;
    
  int sum = list[5] + list.at(7);
}

int main( void )
{
  qDebug() << "Fill and print";
  fillAndPrint();
  
  qDebug() << "Const iterators";  
  constIterators();
  
  qDebug() << "Mutable iterators";
  mutableIterators();

  qDebug() << "Insert and print";
  insertAndPrint();  

  return 0;
}

…I got the error that I wouldn’t have installed QList:

$ LC_ALL=C g++ -Wall -g -o e qlist.cpp
qlist.cpp:32:10: fatal error: QList: No such file or directory
   32 | #include <QList>
      |          ^~~~~~~
compilation terminated.

I searched for a package containing QList, but couldn’t find any. Is there such a package for apt (my package manager)?

2

Answers


  1. Direct call to the compiler is good to test simple hello-world programs, but become soon unmanageable when using libraries. I believe that the problem that you are facing is because g++ does not know where to find Qt.

    Use some project manager, like cmake:

    1. First, make sure that you have the required packages installed.

      $ sudo apt install cmake qt6-base-dev build-essential
      
    2. Create a simple CMakeLists.txt file at the root of your project (Note: the name matters, it should be exactly CMakeLists.txt:

      touch CMakeLists.txt
      

      With the following content:

      cmake_minimum_required(VERSION 3.16)
      
      project(QList)
      
      find_package(Qt6 COMPONENTS Core REQUIRED)
      
      add_executable(QList qlist.cpp)
      target_link_libraries(QList PRIVATE Qt6::Core)
      

      This file tells the following:

      • To create a project named QList
      • To build an executable called "QList"
      • To add qlist.cpp as a source to QList
      • To search for Qt6 library in your system, and to link to it the QList executable.
    3. Build your project:

      mkdir -p build & cd build
      cmake ..
      cmake --build -j 10
      
    4. Execute:

      ./QList
      

    Note: I am assuming that you have Bookworm version12, otherwise, qt6 might still not be available. In that case, use Qt5 instead.

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  2. I searched for a package containing QList, but couldn’t find any

    apt-file is your friend:

    $ apt-file search QList | grep "QList$"
    qt6-base-dev: /usr/include/x86_64-linux-gnu/qt6/QtCore/QList
    qtbase5-dev: /usr/include/x86_64-linux-gnu/qt5/QtCore/QList
    qtbase5-gles-dev: /usr/include/x86_64-linux-gnu/qt5/QtCore/QList
    

    Once qtbase5-dev is installed you can use pkg-config to grab appropriate compiler & linker flags:

    $ pkg-config --list-all | grep -i qt
    Qt5PrintSupport                Qt5 PrintSupport - Qt PrintSupport module
    Qt5Network                     Qt5 Network - Qt Network module
    Qt5Core                        Qt5 Core - Qt Core module
    Qt5Widgets                     Qt5 Widgets - Qt Widgets module
    Qt5Gui                         Qt5 Gui - Qt Gui module
    Qt5DBus                        Qt5 DBus - Qt DBus module
    Qt5OpenGLExtensions            Qt5 OpenGLExtensions - Qt OpenGLExtensions module
    Qt5Test                        Qt5 Test - Qt Unit Testing Library
    Qt5Xml                         Qt5 Xml - Qt Xml module
    Qt5OpenGL                      Qt5 OpenGL - Qt OpenGL module
    Qt5Sql                         Qt5 Sql - Qt Sql module
    Qt5Concurrent                  Qt5 Concurrent - Qt Concurrent module
    
    $ pkg-config --cflags --libs Qt5Core
    -DQT_CORE_LIB -I/usr/include/x86_64-linux-gnu/qt5/QtCore -I/usr/include/x86_64-linux-gnu/qt5 -lQt5Core
    

    All together:

    g++ main.cpp -fPIC $(pkg-config --cflags --libs Qt5Core)
    
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