Dear all,

I have the following minimal working example in QtCreator in which I am trying to use Qt together with libjpeg and libjpeg-turbo:

Appplication.pro:
Qt Code: 
  1. QT       += core gui
  2.  
  3. greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
  4.  
  5. TARGET = Application
  6. TEMPLATE = app
  7.  
  8.  
  9. SOURCES += main.cpp\
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main.cpp:
Qt Code: 
  1. #include <QFile>
  2.  
  3. #include <turbojpeg.h>
  4. #include <jpeglib.h>
  5.  
  6. int main(int argc, char *argv[])
  7. {
  8.     // Step 1: disk to qbytearray
  9.     QFile file("example.jpg");
  10.     file.open(QIODevice::ReadOnly);
  11.     QByteArray blob = file.readAll();
  12.     file.close();
  13.  
  14.  
  15.     // Step 2: Trying to use what's declared in jpeglib.h in order to decompress the file which was just read
  16.     struct jpeg_decompress_struct cinfo;
  17.     struct jpeg_error_mgr jerr;
  18.     cinfo.err = jpeg_std_error(&jerr);
  19.     jpeg_create_decompress(&cinfo);
  20.     //...... if the above lines worked, some more code would be added here ....
  21.  
  22.  
  23.     // Step 3: Trying to use what's declared in turbojpeg.h
  24.     long unsigned int _jpegSize;
  25.     unsigned char* _compressedImage;
  26.  
  27.     int jpegSubsamp, width, height;
  28.     unsigned char buffer[width*height*3]; //!< will contain the decompressed image
  29.  
  30.     tjhandle _jpegDecompressor = tjInitDecompress();
  31.     //...... if the above lines worked, some more code would be added here ....
  32.  
  33.     return 0;
  34. }
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Files turbojpeg.h and jpeglib.h are both included in /usr/include on my computer (running Debian Jessie). If I dpkg -l *jpeg*, then I get the following. It's in german, but I guess everybody will be able to figure out, what it means.

Qt Code: 
  1. Gewünscht=Unbekannt/Installieren/R=Entfernen/P=Vollständig Löschen/Halten
  2. | Status=Nicht/Installiert/Config/U=Entpackt/halb konFiguriert/
  3.          Halb installiert/Trigger erWartet/Trigger anhängig
  4. |/ Fehler?=(kein)/R=Neuinstallation notwendig (Status, Fehler: GROSS=schlecht)
  5. ||/ Name                           Version              Architektur          Beschreibung
  6. +++-==============================-====================-====================-=================================================================
  7. un  libjpeg-dev                    <keine>              <keine>              (keine Beschreibung vorhanden)
  8. un  libjpeg-progs                  <keine>              <keine>              (keine Beschreibung vorhanden)
  9. ii  libjpeg-turbo-progs            1:1.3.1-12           amd64                Programs for manipulating JPEG files
  10. un  libjpeg-turbo8                 <keine>              <keine>              (keine Beschreibung vorhanden)
  11. un  libjpeg62                      <keine>              <keine>              (keine Beschreibung vorhanden)
  12. un  libjpeg62-dbg                  <keine>              <keine>              (keine Beschreibung vorhanden)
  13. un  libjpeg62-dev                  <keine>              <keine>              (keine Beschreibung vorhanden)
  14. ii  libjpeg62-turbo:amd64          1:1.3.1-12           amd64                libjpeg-turbo JPEG runtime library
  15. ii  libjpeg62-turbo-dbg:amd64      1:1.3.1-12           amd64                Debugging symbols for the libjpeg-turbo JPEG library
  16. ii  libjpeg62-turbo-dev:amd64      1:1.3.1-12           amd64                Development files for the libjpeg-turbo JPEG library
  17. un  libjpeg7-dev                   <keine>              <keine>              (keine Beschreibung vorhanden)
  18. un  libjpeg8-dev                   <keine>              <keine>              (keine Beschreibung vorhanden)
  19. un  libjpeg9-dev                   <keine>              <keine>              (keine Beschreibung vorhanden)
  20. ii  libopenjpeg5:amd64             1:1.5.2-3            amd64                JPEG 2000 image compression/decompression library - runtime
  21. un  libturbojpeg                   <keine>              <keine>              (keine Beschreibung vorhanden)
  22. ii  libturbojpeg1:amd64            1:1.3.1-12           amd64                TurboJPEG runtime library - SIMD optimized
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In addition, I also compiled libjpeg-turbo-1.4.1 from source as is described here: http://igor-zivkovic.from.hr/BLFS/general/libjpeg.html
I don't know why I did that... Maybe I was just desperate and did not know, what else to do to get it working ...

I am using compiler GCC for 64 bit, which QtCreator auto-detected in /usr/bin.
Compiling the above project gives the following error results:

Qt Code: 
  1. /home/ron/QtCreator/MWElibjpegForQtForum/Application/main.cpp:18: error: undefined reference to `jpeg_std_error'
  2. /home/ron/QtCreator/MWElibjpegForQtForum/Application/main.cpp:19: error: undefined reference to `jpeg_CreateDecompress'
  3. /home/ron/QtCreator/MWElibjpegForQtForum/Application/main.cpp:30: error: undefined reference to `tjInitDecompress'
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I can see in turbojpeg.h that the header seems to be compiled for Windows, as it starts with:
Qt Code: 
  1. #if defined(_WIN32) && defined(DLLDEFINE)
  2. #define DLLEXPORT __declspec(dllexport)
  3. #else
  4. #define DLLEXPORT
  5. #endif
  6. #define DLLCALL
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However, this is not consistent with the typical approach which I have seen a couple of times in tutorials, etc. such as here: https://www.ibm.com/developerworks :/aix/library/au-porting/
Qt Code: 
  1. #ifdef DLLDEFINE
  2.   #define DLLEXPORT __declspec(dllexport)
  3. #else
  4.   #define DLLEXPORT __declspec(dllimport)
  5. #endif
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So, I am kind of confused how the two libs were supposed to be used...

Does anybody have an idea how to get this thing working? Your help is very much appreciated. Thanks!