Added some preprocessor stuff to check if the user is #including

dlib/all/source.cpp into their own .cpp files.  If so they will get a useful
error message.

dlib/algs.h

 // Copyright (C) 2003  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_ALGs_
 #define DLIB_ALGs_
 

dlib/all/source.cpp

@@ -3,6 +3,10 @@
 #ifndef DLIB_ALL_SOURCe_
 #define DLIB_ALL_SOURCe_
 
+#if defined(DLIB_ALGs_) || defined(DLIB_PLATFORm_)
+#include "../dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 // ISO C++ code
 #include "../base64/base64_kernel_1.cpp"
 #include "../bigint/bigint_kernel_1.cpp"
@@ -73,5 +77,8 @@
 
 #endif // DLIB_ISO_CPP_ONLY
 
+
+#define DLIB_ALL_SOURCE_END
+
 #endif // DLIB_ALL_SOURCe_
 

dlib/bridge.h

 // Copyright (C) 2011  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
+
 #ifndef DLIB_BRIdGE_
 #define DLIB_BRIdGE_ 
 

dlib/dlib_basic_cpp_build_tutorial.txt

+#error "Don't write #include <dlib/all/source.cpp> in your code."
+/*
+  In C++, it is generally an error to #include .cpp files.  This is because it
+  can lead to what are called multiply defined symbol errors.  Therefore, you
+  should compile dlib/all/source.cpp into your application just like you would
+  compile any other .cpp file.  
+  
+  If you are using Visual Studio you add .cpp files to your application using
+  the solution explorer window.  Specifically, right click on Source Files,
+  then select Add -> Existing Item and select the .cpp files you want to add.
+
+  For general information on compiling dlib see http://dlib.net/compile.html
+*/

dlib/gui_widgets.h

 // Copyright (C) 2005  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_GUI_WIDGETs_
 #define DLIB_GUI_WIDGETs_
 

dlib/image_io.h

 // Copyright (C) 2006  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_IMAGe_IO_ 
 #define DLIB_IMAGe_IO_
 

dlib/image_processing.h

 // Copyright (C) 2011  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_IMAGE_PROCESSInG_H_h_
 #define DLIB_IMAGE_PROCESSInG_H_h_ 
 

dlib/image_transforms.h

 // Copyright (C) 2006  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_IMAGE_TRANSFORMs_
 #define DLIB_IMAGE_TRANSFORMs_ 
 

dlib/opencv.h

 // Copyright (C) 2009  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_OPEnCV_HEADER
 #define DLIB_OPEnCV_HEADER
 

dlib/platform.h

 // Copyright (C) 2006  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_PLATFORm_
 #define DLIB_PLATFORm_
 

dlib/svm.h

 // Copyright (C) 2007  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_SVm_HEADER
 #define DLIB_SVm_HEADER
 

dlib/svm_threaded.h

 // Copyright (C) 2008  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_SVm_THREADED_HEADER
 #define DLIB_SVm_THREADED_HEADER
 

dlib/threads.h

 // Copyright (C) 2003  Davis E. King (davis@dlib.net)
 // License: Boost Software License   See LICENSE.txt for the full license.
+
+#ifdef DLIB_ALL_SOURCE_END
+#include "dlib_basic_cpp_build_tutorial.txt"
+#endif
+
 #ifndef DLIB_THREADs_
 #define DLIB_THREADs_