I am trying to introduce precompiled headers into my project because of long compile times in my project right now. I have a main project that includes a main function and all the real code is in the DLL project(they are linked together.) I named my precompiled header "vpch.h" and i created a vpch.cpp that includes vpch.h. I am using visual studio 2017 so I went into the properties of vpch.cpp and selected Create. Then I added vpch.h as the first thing in all my cpp files. All files are set to use precompiled headers and reference vpch.h Every CPP files throws the error:
Error C1010 unexpected end of file while looking for precompiled header.
Did you forget to add '#include "vpch.h"' to your source?
I am at a loss as to what to do because I have followed many tutorials and can't find a reason for this. As well as most issues that pop up on google are people just accidentally including precompiled headers.
My only thought is that maybe in the section in properties where it asks for the name of the precompiled header, I need to do more than put "vpch.h" and maybe an exact file location? Any help with this is super appreciated.
EDIT
From further debugging it would appear that all but ONE cpp file is throwing an error. The one that doesn't throw an error is the one that exists in the same exact folder as the vpch.h. So files that can't just write #include "vpch.h" and have to write something like "../vpch.h" I can write #include <vpch.h> and I am going to try that now but I am unsure that will help.
The issue was with every CPP file that wasnt in the same folder as the precompiled header.
So if you use a file structure that contains different classes in different folders, using
#include "../../vpch.h" will actually fail. You must add the root folder to your additional include directories and then use #include <vpch.h> for all files. I can NOT tell you why using #include "../../vpch.h" wasn't working. It seems counter intuitive for it to fail in my opinion.
It may be because it searches for the precompiled header in the same folder as the file you are referencing it in. This answer, however, will work as a solution.
So a few hours ago I started learning c++ in codelite but I was getting frustated with, so I just got codeblocks and imported the project. But now whenever I try to compile it returns:
fatal error: imports.h: No such file or directory
This is my project hierarchy in codeblocks:
And this is what the project folder looks like:
What am I doing wrong?
I know this is years later, but I've recently seen students following what I deem is frankly bad advice such as what is given above. For those learning c++ this functionality is NOT for you. To add headers you should simply check that you are using double quotes, instead of angled brackets i.e.
#include "myheader.h"
and NOT
#include <myheader.h>
Angled brackets are meant for libraries (informally) and adding a simple header file for you basic classes does not require you to change default search directories. The problem comes when someone else tries to run your code (assuming you're doing this for uni) and their IDE isn't setup to search for a "library" (your header) where it shouldn't be. Double quotes tells the compiler the files exist in your current relative directory. This way you can keep your main, headers and header implementation in one directory. Fiddling with your IDE should only be done when necessary. KISS
You have to tell Codeblocks where to find the header files that you include. Try adding the full path to your '/Headers' in the include directories of codeblocks
Goto 'Codeblocks menu > Settings > Compiler > Search directories > Add'.
EDIT: Since your issue, however, is quite irrelevant to learning the C++ language itself, I suggest that you start with simpler programs, then move on to more complex ones. That, of course, unless you have previous experience with other programming languages
Since I haven't found any Makro for
#define 'hostname of device where compiler is located' // which is unique and not to be copied !
I have now successfully used and included
#include "myCompileEnv.h"
as a workaround with the comments above, which is located more central - above the project directories in CodeBlocks.
I'm using a header only library for a project (glm) and am currently trying to debug some problems I'm having. I trust that glm is giving me the correct values, however it is dog slow when built without optimisations (I'm using visual studio 2012/2013/2010 whichever is easiest to do this in, as all 3 are installed).
Is there a way to enable optimisations (specifically /O2), and disable debug symbols for just the GLM header files, while retaining the debug information for the rest of the solution?
EDIT:
I'd like to throw in, that I'd rather not change libraries at this point, as it's almost at the end of the project and I have other things to do aswell, so rewriting to use Eigen/CML isn't really on the table.
You can try:
1) Create one code file and include all headers you need.
2) Define all the template classes in this source file you want to use (e.g. "template ClassA;"
3) Compile this source File with optimization and link later against it.
4) Create a header file and declare all theses classes without the function definitions (simply copy the original header files and erase all functions definitions.)
5) Use this header file for your project.
I'm having several "undefined reference" (during linkage) and "unresolved symbol" (during runtime after dlopen) issues where I work. It is quite a large makefile system.
Are there general rules and guidelines for linking libraries and using compiler flags/options to evade these types of errors?
IF YOU WERE USING MSVC :
You cannot evade this type of error by setting a flag : it means some units (.cpp) dont' have definitions of declared identifiers. It's certainly caused by missing includes or missing object definitions (often static objects) somewhere.
While developing you can follow those guidelines ( from those articles ) to be sure all your cpp includes all the headers they need but no more :
Every cpp file includes its own header file first. This is the most
important guideline; everything else
follows from here. The only exception
to this rule are precompiled header
includes in Visual Studio; those
always have to be the first include in
the file. More about precompiled
headers in part two of this article.
A header file must include all the header files necessary to parse it.
This goes hand in hand with the first
guideline. I know some people try to
never include header files within
header files claiming efficiency or
something along those lines. However,
if a file must be included before a
header file can be parsed, it has to
be included somewhere. The advantage
of including it directly in the header
file is that we can always decide to
pull in a header file we’re interested
in and we’re guaranteed that it’ll
work as is. We don’t have to play the
“guess what other headers you need”
game.
A header file should have the bare minimum number of header files
necessary to parse it. The previous
rule said you should have all the
includes you need in a header file.
This rule says you shouldn’t have any
more than you have to. Clearly, start
by removing (or not adding in the
first place) useless include
statements. Then, use as many forward
declarations as you can instead of
includes. If all you have are
references or pointers to a class, you
don’t need to include that class’
header file; a forward reference will
do nicely and much more efficiently.
But as commenter have suggested, it seem you're using g++...
Setting up a build system where X depends on Y which depends on Z helps. It's when you get into circles (Z depends on X) that things get ugly.
Oftentimes it's the order libraries are linked ("-lZ -lY -lX" vs "-lX -lY -lZ") that causes grief. More rarely, you have the same library-name in multiple places on your search path, or your linking against outdated versions that have not yet been recompiled.
"nm --demangle" can let you see where things are defined/used.
"ldd" can be used to see what dynamic libraries you depend on.
The gcc/g++ flag -print-file-name=LIBRARY can help track down exactly which library is being used.
Afterthought: (Since you ask about rules/guidelines.)
It is possible to set up a makefile system such that:
If module=D depends on modules A,B,&C.
Then trying to make module=D would first make modules A,B,&C.
And, more importantly, module=D would automatically determine its libraries (-lA,etc), library paths (-LA), and include paths (-IA) from the makefiles for modules A,B,&C.
That can get a little hairy to set up. Last time I did it, I favored merely caching the information rather than forking an excessive number of make subprocesses. Coupled with makefile-importing and a little perl script to remove duplicates. Kludgey, I know. (Powers that be didn't want to spend time on infrastructure.) But it can be done.
Then again, I was using GNU-make, which has a few extensions.
I am working on a large C++ project in Visual Studio 2008, and there are a lot of files with unnecessary #include directives. Sometimes the #includes are just artifacts and everything will compile fine with them removed, and in other cases classes could be forward declared and the #include could be moved to the .cpp file. Are there any good tools for detecting both of these cases?
While it won't reveal unneeded include files, Visual studio has a setting /showIncludes (right click on a .cpp file, Properties->C/C++->Advanced) that will output a tree of all included files at compile time. This can help in identifying files that shouldn't need to be included.
You can also take a look at the pimpl idiom to let you get away with fewer header file dependencies to make it easier to see the cruft that you can remove.
PC Lint works quite well for this, and it finds all sorts of other goofy problems for you too. It has command line options that can be used to create External Tools in Visual Studio, but I've found that the Visual Lint addin is easier to work with. Even the free version of Visual Lint helps. But give PC-Lint a shot. Configuring it so it doesn't give you too many warnings takes a bit of time, but you'll be amazed at what it turns up.
There's a new Clang-based tool, include-what-you-use, that aims to do this.
!!DISCLAIMER!! I work on a commercial static analysis tool (not PC Lint). !!DISCLAIMER!!
There are several issues with a simple non parsing approach:
1) Overload Sets:
It's possible that an overloaded function has declarations that come from different files. It might be that removing one header file results in a different overload being chosen rather than a compile error! The result will be a silent change in semantics that may be very difficult to track down afterwards.
2) Template specializations:
Similar to the overload example, if you have partial or explicit specializations for a template you want them all to be visible when the template is used. It might be that specializations for the primary template are in different header files. Removing the header with the specialization will not cause a compile error, but may result in undefined behaviour if that specialization would have been selected. (See: Visibility of template specialization of C++ function)
As pointed out by 'msalters', performing a full analysis of the code also allows for analysis of class usage. By checking how a class is used though a specific path of files, it is possible that the definition of the class (and therefore all of its dependnecies) can be removed completely or at least moved to a level closer to the main source in the include tree.
I don't know of any such tools, and I have thought about writing one in the past, but it turns out that this is a difficult problem to solve.
Say your source file includes a.h and b.h; a.h contains #define USE_FEATURE_X and b.h uses #ifdef USE_FEATURE_X. If #include "a.h" is commented out, your file may still compile, but may not do what you expect. Detecting this programatically is non-trivial.
Whatever tool does this would need to know your build environment as well. If a.h looks like:
#if defined( WINNT )
#define USE_FEATURE_X
#endif
Then USE_FEATURE_X is only defined if WINNT is defined, so the tool would need to know what directives are generated by the compiler itself as well as which ones are specified in the compile command rather than in a header file.
Like Timmermans, I'm not familiar with any tools for this. But I have known programmers who wrote a Perl (or Python) script to try commenting out each include line one at a time and then compile each file.
It appears that now Eric Raymond has a tool for this.
Google's cpplint.py has an "include what you use" rule (among many others), but as far as I can tell, no "include only what you use." Even so, it can be useful.
If you're interested in this topic in general, you might want to check out Lakos' Large Scale C++ Software Design. It's a bit dated, but goes into lots of "physical design" issues like finding the absolute minimum of headers that need to be included. I haven't really seen this sort of thing discussed anywhere else.
Give Include Manager a try. It integrates easily in Visual Studio and visualizes your include paths which helps you to find unnecessary stuff.
Internally it uses Graphviz but there are many more cool features. And although it is a commercial product it has a very low price.
You can build an include graph using C/C++ Include File Dependencies Watcher, and find unneeded includes visually.
If your header files generally start with
#ifndef __SOMEHEADER_H__
#define __SOMEHEADER_H__
// header contents
#endif
(as opposed to using #pragma once) you could change that to:
#ifndef __SOMEHEADER_H__
#define __SOMEHEADER_H__
// header contents
#else
#pragma message("Someheader.h superfluously included")
#endif
And since the compiler outputs the name of the cpp file being compiled, that would let you know at least which cpp file is causing the header to be brought in multiple times.
PC-Lint can indeed do this. One easy way to do this is to configure it to detect just unused include files and ignore all other issues. This is pretty straightforward - to enable just message 766 ("Header file not used in module"), just include the options -w0 +e766 on the command line.
The same approach can also be used with related messages such as 964 ("Header file not directly used in module") and 966 ("Indirectly included header file not used in module").
FWIW I wrote about this in more detail in a blog post last week at http://www.riverblade.co.uk/blog.php?archive=2008_09_01_archive.xml#3575027665614976318.
Adding one or both of the following #defines
will exclude often unnecessary header files and
may substantially improve
compile times especially if the code that is not using Windows API functions.
#define WIN32_LEAN_AND_MEAN
#define VC_EXTRALEAN
See http://support.microsoft.com/kb/166474
If you are looking to remove unnecessary #include files in order to decrease build times, your time and money might be better spent parallelizing your build process using cl.exe /MP, make -j, Xoreax IncrediBuild, distcc/icecream, etc.
Of course, if you already have a parallel build process and you're still trying to speed it up, then by all means clean up your #include directives and remove those unnecessary dependencies.
Start with each include file, and ensure that each include file only includes what is necessary to compile itself. Any include files that are then missing for the C++ files, can be added to the C++ files themselves.
For each include and source file, comment out each include file one at a time and see if it compiles.
It is also a good idea to sort the include files alphabetically, and where this is not possible, add a comment.
If you aren't already, using a precompiled header to include everything that you're not going to change (platform headers, external SDK headers, or static already completed pieces of your project) will make a huge difference in build times.
http://msdn.microsoft.com/en-us/library/szfdksca(VS.71).aspx
Also, although it may be too late for your project, organizing your project into sections and not lumping all local headers to one big main header is a good practice, although it takes a little extra work.
If you would work with Eclipse CDT you could try out http://includator.com to optimize your include structure. However, Includator might not know enough about VC++'s predefined includes and setting up CDT to use VC++ with correct includes is not built into CDT yet.
The latest Jetbrains IDE, CLion, automatically shows (in gray) the includes that are not used in the current file.
It is also possible to have the list of all the unused includes (and also functions, methods, etc...) from the IDE.
Some of the existing answers state that it's hard. That's indeed true, because you need a full compiler to detect the cases in which a forward declaration would be appropriate. You cant parse C++ without knowing what the symbols mean; the grammar is simply too ambiguous for that. You must know whether a certain name names a class (could be forward-declared) or a variable (can't). Also, you need to be namespace-aware.
Maybe a little late, but I once found a WebKit perl script that did just what you wanted. It'll need some adapting I believe (I'm not well versed in perl), but it should do the trick:
http://trac.webkit.org/browser/branches/old/safari-3-2-branch/WebKitTools/Scripts/find-extra-includes
(this is an old branch because trunk doesn't have the file anymore)
If there's a particular header that you think isn't needed anymore (say
string.h), you can comment out that include then put this below all the
includes:
#ifdef _STRING_H_
# error string.h is included indirectly
#endif
Of course your interface headers might use a different #define convention
to record their inclusion in CPP memory. Or no convention, in which case
this approach won't work.
Then rebuild. There are three possibilities:
It builds ok. string.h wasn't compile-critical, and the include for it
can be removed.
The #error trips. string.g was included indirectly somehow
You still don't know if string.h is required. If it is required, you
should directly #include it (see below).
You get some other compilation error. string.h was needed and isn't being
included indirectly, so the include was correct to begin with.
Note that depending on indirect inclusion when your .h or .c directly uses
another .h is almost certainly a bug: you are in effect promising that your
code will only require that header as long as some other header you're using
requires it, which probably isn't what you meant.
The caveats mentioned in other answers about headers that modify behavior
rather that declaring things which cause build failures apply here as well.