I am looking for a straight forward way to use precompiled headers for a C++ project using Eclipse / CDT. The stuff does work when running from command line but I am looking for an easy way to integrate it into Eclipse.
Any suggestions ?!
Just to help others who may stumble upon this (since i spent some time figuring this out)
The first thing to do is create a PCH folder (if you want) with a pch.cpp and pch.h file.
pch.cpp: (this file is to compile the .gch)
#include "pch.h"
pch.h:
#include <iostream>
#include <string>
// more stuff that's not changing anytime soon...
The second thing to do is create a PCH build configuration.
exclude all your project source files from this build. (we only need to compile pch.cpp)
select the files/folders > Right Click > Resource Configurations > Exclude from Build > PCH
Now we need to make it compile as a .gch (precompiled header)
pch.cpp > Right Click > Properties > C/C++ Build > Settings > Tool Settings
Compiler > Pattern: ${COMMAND} ${FLAGS} ${INPUTS} (remove all the output stuff)
Misc > Flags: -c -x c++-header -o "../src/PCH/pch.h.gch"
Now when you build with this configuration, it'll produce the pch.h.gch where pch.h is.
(it'll also give a meaningless error trying to create an exe. just ignore that)
Back on the normal Release build, exclude pch.cpp since you don't need to compile that.
Now it's time to test the .gch is being used over the .h
at the top of pch.h put #error "not using precompiled header file"
The .ghc is only used if the header is included first, in the compiling file.
"Only one precompiled header can be used in a particular compilation."
you should precompile different selections of headers best fit for different compilation units
COMPILE TESTS
without precompiled headers
took 34s.189ms output src=2,143,078 bytes exe=1,346,864 bytes
with -include ../src/PCH/pch.h (included in every compilation unit) (only the pch.h not the .gch)
took 48s.364ms output src=2,159,431 bytes exe=1,355,298 bytes
(this is why we #include manually where needed so it should still take around 34s to compile without .gch)
with -include ../src/PCH/pch.h and pch.h.gch (fast compilation, but still inefficient with -include)
took 22s.535ms output src=2,159,431 bytes exe=1,355,298 bytes
if the pch's are organized/utilized properly (correct choice of headers and files to include them in) (not used in every file) it should be much faster than 22s. (this test was just done on a project which weren't built with pch's in mind)
additional speedup which can triple compile time
Project > Properties > C/C++ Build > Behavior > Enable parallel build
From what i've seen, currently Eclipse CDT doesn't support precompiled headers directly. I mean, you can't set an option like : "For this header, compile it". The same applies for headers of external libraries of your eclipse project.
As you know, you need to set the same compilers flag for the header compilation in order to get the compiler use it for the other compilation unit. (At least in the case of GCC).
So, you have several solutions :
You replace the default build command found in "Properties for -> C/C++ Build -> Builder Settings -> Build command" with a custom script that will modify the makefiles generated by eclipse and then call make. A ruby solution is proposed here. Note, that it doesn't allow the use of multiple precompiled headers.
You can use ccache instead of using GCC. It detects when the same compilation is done again, so it's a bit different from using precompiled headers.
EDIT :
To get the ruby script working, you need to have at least one .cpp file inside the same directory as your header file. Otherwise you'll get an error on a missing file "subdir.mk".
Another approach is to create a source file (e.g. pch.cpp) with build settings changed to create the precompiled header. It should be included in the build in order to create the precompiled header, and then excluded in order to build the final executable. It needs to be temporarily reincluded if the header file is changed.
This website provides more details, including a way of creating different precompiled headers for each build configuration.
Consider using cmake and cotire
Related
When I build my c++ solution in Visual Studio it complains that the xxxxx.pch file is missing. Is there a setting I am missing to get the pre-compiled headers back?
here is the exact error for completeness:
Error 1 fatal error C1083: Cannot open precompiled header file: 'Debug\xxxxx.pch': No such file or directory
NOTE: Later versions of the IDE may use "pch" rather than "stdafx" in the default names for related files. It may be necessary to substitute pch for stdafx in the instructions below. I apologize. It's not my fault.
Right-click on your project in the Solution Explorer.
Click Properties at the bottom of the drop-down menu.
At the top left of the Properties Pages,
select All Configurations from the drop-down menu.
Open the C/C++ tree and select Precompiled Headers
Precompiled Header: Select Use (/Yu)
Fill in the Precompiled Header File field. Standard is stdafx.h
Click Okay
If you do not have stdafx.h in your Header Files put it there. Edit
it to #include all the headers you want precompiled.
Put a file named stdafx.cpp into your project. Put #include "stdafx.h"
at the top of it, and nothing else.
Right-click on stdafx.cpp in Solution Explorer. Select Properties
and All configurations again as in step 4 ...
... but this time select Precompiled Header Create (/Yc). This will only
bind to the one file stdafx.cpp.
Put #include "stdafx.h" at the very top of all your source files.
Lucky 13. Cross your fingers and hit Build.
Precompiled Header (pch) use is a two-step process.
In step one, you compile a stub file (In VS200x it's usually called stdafx.cpp. Newer versions use pch.cpp.). This stub file indirectly includes only the headers you want precompiled. Typically, one small header (usually stdafx.h or pch.hpp) lists standard headers such as <iostream> and <string>, and this is then included in the stub file. Compiling this creates the .pch file.
In step 2, your actual source code includes the same small header from step 1 as the first header. The compiler, when it encounters this special header, reads the corresponding .pch file instead. That means it doesn't have to (re)compile those standard headers every time.
In your case, it seems step 1 fails. Is the stub file still present? In your case, that would probably be xxxxx.cpp. It must be a file that's compiled with /Yc:xxxxx.pch, since that's the compiler flag to indicate it's step 1 of the PCH process. If xxxxx.cpp is present, and is such a stub file, then it's probably missing its /Yc: compiler option.
Fix:
Make sure you have xxxxx.cpp in your project
Compile xxxxx.cpp with /Yc flag (Create Precompiled Header)
(right click on xxxxx.cpp -> properties -> Precompiled Headers -> create)
Compile all other files with /Yu flag (Use Precompiled Header)
(right click on project -> properties -> Precompiled Headers -> use)
Right click to the project and select the property menu item
goto C/C++ -> Precompiled Headers
Select Not Using Precompiled Headers
Yes it can be eliminated with the /Yc options like others have pointed out but most likely you wouldn't need to touch it to fix it. Why are you getting this error in the first place without changing any settings? You might have 'cleaned' the project and than try to compile a single cpp file. You would get this error in that case because the precompiler header is now missing. Just build the whole project (even if unsuccessful) and than build any single cpp file and you won't get this error.
In case this is happening to you on a server build (AppCenter) and yo uaer using CocoaPods ensure that your Podfile is checked in.
AppCenter only runs the "pod install" command if it finds a Pofile and it DOES NOT find the PODS folder on the files.
I had the folder checked-in, but because git automatically ignores .pch files (check you .gitignore to veryfy this), my .pch weren'nt being checked in.
I sorted my issue by forcing the .pch files to check it, but Deleting the PODS folder should work too, since Appcenter will run the pod install command in that case.
Hoppefully this helps somebody.
VS screwed (mine is 2019 ;( ).
Go ahead and choose "not using precompiled headers" as other guys are pointing out then open the project file (vcxproj) with any text editor, and delete the outlined two entries in two places. Enjoy cleaning up the mess!
As a matter of fact, the 'pch.h' entry in the vcxproj file you see it below, you will ever find it in VS properties' interfaces.
Try Build > Clean Solution, then Build > Build Solution. This works for me.
I know this topic is very old, but I was dealing with this in VS2015 recently and what helped was to deleted the build folders and re-build it. This may have happen due to trying to close the program or a program halting/freezing VS while building.
I was searching for the iOS PCH file having the same problem, if you got here like me too, the solution that I've found is by clearing derived data; Close Simulator(s), go to xCode prefs -> locations -> go to the derived data file path, close xCode, delete the files in the derived data folder, re launch and cheers :)
I managed to create this problem for myself because I wanted to use a pch.h and pch.cpp file from different directories. So, I deleted the two files from my project and then added them as existing files from somewhere else. Big mistake as precompiled header files can no longer be found.
There is no way that I can find to fix the problem from the Visual Studio 2019 UI. You must edit the project file and make sure the following look like this:
<ClCompile Include="pch.cpp">
<PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">Create</PrecompiledHeader>
<PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">Create</PrecompiledHeader>
<PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">Create</PrecompiledHeader>
<PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|x64'">Create</PrecompiledHeader>
</ClCompile>
I had same issue, and I managed to solve it like this:
ERROR :
fatal error C1083: Cannot open precompiled header file : "Debug\myProj.pch". No such file or directory
first one is when I had an error,
and changed it like a second picture
make (/Yx)
myProj.h
In my case, it was necessary to select Create (/Yu), instead of the standard Use (/Yu)
to
If everything is right, but this mistake is present, it need check next section in ****.vcxproj file:
<ClCompile Include="stdafx.cpp">
<PrecompiledHeader Condition=
In my case it there was an incorrect name of a configuration: only first word.
I'm using a library written by others which is kinda based on C for C++ usage -I think-. All inclusions used inside the headers or source files are in the form <> instead of "" even though they are not standard library files. My compiler doesn't recognize them and returns error "file not found"
An example of the problem is inside the following header:
#ifndef _ga_ga_h_
#define _ga_ga_h_
// Make sure that we get the configuration into each of the galib components
// that will be used.
#include <ga/gaconfig.h>
// These are the headers for all of the genetic algorithm classes.
#include <ga/GASimpleGA.h>
#include <ga/GASStateGA.h>
#include <ga/GAIncGA.h>
#include <ga/GADemeGA.h>
#include <ga/GADCrowdingGA.h>
// Here we include the headers for all of the various genome types.
#include <ga/GA1DBinStrGenome.h>
#include <ga/GA2DBinStrGenome.h>
#include <ga/GA3DBinStrGenome.h>
#include <ga/GABin2DecGenome.h>
I include that header inside my program using #include "ga.h" but it is very hard to change inside every header/source file in the library.
Is there a way to make the compiler use <> as if they were ""?
I tried adding the paths to "Addition include directories"from Project properties (I'm using Visual Studio), Many inclusions' errors disappeared but around 30 persisted. The strange thing is that they are in a file called "c1xx" but i don't have that file!!
thanks,
The definition is somewhat that <> is used for "system" header files, usually found in locations like /usr/include (on Unix-like systems) and "" is used for local header files. When you compile your code, you can indicate the location of additional directories containing header files e.g. using the -I option when using GCC. Check your compiler's documentation for the setting needed
So, e.g. on Linux and GCC, if your "ga" directory is in /usr/local/include/ga, you would use cc -I /usr/local/include.
This indeed looks like a problem of telling the compiler where to look for the included header files. As mentioned in the other answers, when you do a #include <header.h>, header.h must be in one of the include search paths - either the system includes, or the additional paths that you are telling the compiler to look for headers. In Linux/g++ (as mentioned in the other answers here), you do that by passing in the the additional search paths in the -I flag. The compilation command would look something like:
g++ -I/additional/header/search/path -o a.out your_file.cpp
Since you are using visual studio and the MSVC compiler, the equivalent would be the /I flag, and the compilation command would look something like:
CL /I\additional\header\path your_file.cpp
I am assuming you are using Visual Studio - you can also configure that from the project properties. Go to Configuration Properties > C/C++ > General and modify Additional Include Directories. Refer these for more info:
Setting C++ compiler and build properties
Additional include directories
First about the difference between <header> and <file>. The standards (both C and C++) only specifies that
#include <header>
includes an header named header and that
#include "file"
includes a source file named file, if none is found an header named file is included instead.
What are headers and how they differ from source files is left to the implementation. In practice they are files as well. So #include <header> is looking for a file in some places, #include "file" is looking for a file in some other places and if not found at the same places as for #include <file>.
AFAIK all compilers
are able to search for source files in the directory of the file containing the include directive
are able to be given a list of directories to search for headers before their default search path.
ISTR that Visual C++ is also searching for a source file in the directories of files indirectly including it. (I can't confirm currently if my memory is good; that behavior is AFAIK unachievable with other compilers so I never relied on it and -- by luck? -- it never resulted in a different behavior for my programs).
Obviously that behavior is more or less customizable. For instance with g++ is possible to:
disable the search of a source file in the directory of the file containing the include directive (with -I-, note that -I- is deprecated since gcc 4.0 -- 2005 -- when -iquote has been introduced and there is no non-deprecated way to achieve this)
to add a list of directories to search for source files and not for headers (with -iquote and it's an effect of -I- as well)
to give a list of directories to search for headers after the default list of directories (with -idirafter)
to give a list of directories to search for headers which are processed specially (with -isystem; less warnings are given for constructs in those files which help when using the "treat warnings as errors" flags, they aren't considered as dependencies with -MM and -MMD which usually is a nuisance)
Now for your problem. The library has been visibly designed to be used by adding the directory containing the directory ga to the include path. That should be enough as I'm unaware of any compiler modifying its search path for headers depending on how the file including the header has been included.
Note that c1xx is probably the name of the compiler executable, not the name of a file trying to include another (again, I'm not in position to ensure that's the case now, but compare with cc1plus which is the name of the compiler for GCC -- g++ is a driver handling several things and executing cc1plus to handle the compilation of C++ code)
If you do on the command line:
echo | gcc -v -E -x c++ -
You will get an output with the default include directories for C++. Those are the built in system's include search paths.
If you compile with g++ -I/some/dir -o foo foo.cpp, you are adding an additional include search path (/some/dir) to the compilation.
Headers in the above locations can be found by include directives like #include <header>. #include "header" directives can also find headers in those locations, but they are more relevant for the following case.
When you do #include "header", your compiler will first try to find "header" relative to the directory of foo.cpp if it includes it, despite foo.cpp directory being in search paths or not. If it doesn't find it there, it will try to look up in the include search paths. So this one is more relevant for headers that are more tied to a specific .cpp file and you don't want additional include search paths added to the compilation, or if you prefer to use include directives with relative paths.
So if you use #include <header>, header must be in some of the include search paths, system or /some/dir from -I flag. If header is relative to foo.cpp, but not in search paths, compilation will fail.
If you use #include "header" and header is not in any of the include search paths, it can still be found relative to foo.cpp location.
I have a project in C++ that I would like to view the preprocessor output to see what some #defines and macros would look like. I tried the /p switch to turn on the preprocess to a file option to the compiler (it turns off full compilation and only runs the preprocessor) but my project now refuses to compile and shows a long list of errors starting with:
"Cannot open include file: 'stdafx.h': No such file or directory".
The project compiles fine without the /p argument, of course. Any suggestions?
If you run cl.exe on its own then you would need to supply all the same parameters as the IDE does when building, otherwise it can't find all the include paths and preprocessor macros. However, there is another way to do this. In the project file, select the .cpp file you want, and choose Properties > C++ > Preprocessor > Generate preprocessor file. Then compile the .cpp file.
This will generate the preprocessed file (file.i I think) in the output directory. It's a shame there isn't an easier way of just selecting a file and hitting 'preprocess' but this could probably be done quite easily with a VisualStudio macro. Don't forget to set the option back afterwards.
Are all the other options (like /I) still the same when you compile with /p? It sounds like it's not picking up your header files. Alternately because it's trying to pre-process all the includes it's no longer generating the stdafx.h precompiled header - you could try just including all the needed headers directly instead of that.
From this thread
http://www.codeguru.com/forum/showthread.php?p=1863547
It seems this cannot be done with:
#pragma comment(linker, "/out:mycool.exe")
Is there some simple way this can be done without having to use project settings, make files etc?
Added:
Why do I want to do this.
Well this gets into another subject which is probably my next question - working with the IDE.
I have to provide many examples in one project. They are simple single files that demonstrate different ways of doing things and each one should really be a different executable EXample1.exe, Example2.exe.
I only want to paste the source code or hand someone a SINGLE file with everything needed to make the example executable (on a web forum for example. I do not want to attach a 3.6MB project folder just to get a different executable name!
Compiling transcends source code. Source code only exists, and something has to take it and make something of it. Anything you do in source code is really just going to be a directive to the compiler. You might as well use project settings. This stuff isn't standard, because the standard only covers behavior and definitions of source code, not compilers.
g++ takes the output file as a parameter: g++ -o myexe.exe main.cpp. What should it do if it comes across a "output should be this!" directive in the source code?
Same with cl (Visual Studio), it passes the output setting into the command line.
Not to say it's impossible, but I doubt it's worth it to try and come up with a way to do it, let alone make it standard.
To use the linker pragma comment, the output file must NOT be specified in the linker section of the project properties:
project -> properties -> Linker -> General -> Output File
Delete the entry: $(OutDir)\$(ProjectName).exe
then the prama statement will work:
pragma comment(linker, "/out:mycool.exe")
Thanks to JC for the walkthrough
Specifying a complete path is not possible
http://social.msdn.microsoft.com/forums/en-US/vcgeneral/thread/11a06ecd-dcca-4d81-8626-ba0c5a1835c1/
but the work around is:
What I do is have a header file loacated somewhere near the library file, this header will include the pragma line.
pragma comment(lib, FILE "../libs/mylibary.lib")
if FILE is "C:\Project\SharedLibs\Xvid\latest.h"
then the pragma will include
"C:\Project\SharedLibs\Xvid\libs/mylibary.lib" once it has normalized the uri to remove the ..'s
this will always cause the pragma to include the library with an absolute path created from the path of the accompanying header.
I use this system to include a single header in a project and regardless of the relative paths between the lib and project the lib will always be included cleanly.
Added:
The full path can be specified as long as it is 8.3 format. This can present problems for a path like:
C:\Program Files\Abyss Web Server\htdocs\
Program files is commonly Progra~1
but a folder name with a space is more tricky. In this case it becomes AbyssW~1
The \ must be escaped resulting in \ producing a working pragma of:
#pragma comment(linker, "/out:C:\\Progra~1\\AbyssW~1\\htdocs\\MyApp.exe")
as kibibu showed:
#pragma comment(linker, "/out:\"C:\\Program Files\\Abyss Web Server\\htdocs\\MyApp.exe\"")
also works
If you don't want to stray too far from a stock Visual C++ installation, you should consider using NMake. It can integrate with the IDE using project files, but it can also simply be run from the command-line very easily. It's also far more lightweight than project files for generating an arbitrary number of simple and similar executables.
I have a Visual Studio C++ based program that uses pre-compiled headers (stdafx.h). Now we are porting the application to Linux using gcc 4.x.
The question is how to handle pre-compiled header in both environments.
I've googled but can not come to a conclusion.
Obviously I want leave stdafx.h in Visual Studio since the code base is pretty big and pre-compiled headers boost compilation time.
But the question is what to do in Linux. This is what I found:
Leave the stdafx.h as is. gcc compiles code considerable faster than VC++ (or it is just my Linux machine is stronger ... :) ), so I maybe happy with this option.
Use approach from here - make stdafx.h look like (set USE_PRECOMPILED_HEADER for VS only):
#ifdef USE_PRECOMPILED_HEADER
... my stuff
#endif
Use the approach from here - compile VC++ with /FI to implicitly include stdafx.h in each cpp file. Therefore in VS your code can be switched easily to be compiled without pre-compiled headers and no code will have to be changed.
I personally dislike dependencies and the mess stdafx.h is pushing a big code base towards. Therefore the option is appealing to me - on Linux you don't have stdafx.h, while still being able to turn on pre-compiled headers on VS by /FI only.
On Linux compile stdafx.h only as a precompiled header (mimic Visual Studio)
Your opinion? Are there other approaches to treat the issue?
You're best off using precompiled headers still for fastest compilation.
You can use precompiled headers in gcc as well. See here.
The compiled precompiled header will have an extension appended as .gch instead of .pch.
So for example if you precompile stdafx.h you will have a precompiled header that will be automatically searched for called stdafx.h.gch anytime you include stdafx.h
Example:
stdafx.h:
#include <string>
#include <stdio.h>
a.cpp:
#include "stdafx.h"
int main(int argc, char**argv)
{
std::string s = "Hi";
return 0;
}
Then compile as:
> g++ -c stdafx.h -o stdafx.h.gch
> g++ a.cpp
> ./a.out
Your compilation will work even if you remove stdafx.h after step 1.
I used option 3 last time I needed to do this same thing. My project was pretty small but this worked wonderfully.
I'd either go for option 4 or option 2. I've experimented with precompiled headers on both various VS versions and GCC on Linux (blog posts about this here and here). In my experience, VS is a lot more sensitive to the length of the include paths, number of directories in the include path and the number of include files than G++ is. When I measured build times properly arranged precompiled headers would make a massive difference to the compile time under VS whereas G++ was pretty much unimpressed by this.
Actually, based on the above what I did the last time I worked on a project where this was necessary to rein in the compile time was to precompile the equivalent of stdafx.h under Windows where it made sense and simply used it as a regular file under Linux.
Very simple solution.
Add a dummy file entry for "stdafx.h" in Linux environment.
I would only use option 1 in a big team of developers.
Options 2, 3, and 4 will often halt the productivity of other members of your team, so you can save a few minutes a day in compile time.
Here's why:
Let's assume that half of your developers use VS and half use gcc.
Every now and then some VS developer will forget to include a header in a .cpp file.
He won't notice, because the stdafx.h implicitly includes it. So, he pushes his changes in the version control, and then a few other members of the gcc team will get compiler errors.
So, for every 5 minutes-a-day you gain by using precompiled headers, 5 other people waste by fixing your missing headers.
If you don't share the same code across all of your compilers, you will run into problems like that every day. If you force your VS developers to check for compilation on gcc before pushing changes, then you will throw away all your productivity gains from using precompiled headers.
Option 4 sounds appealing, but what if you want to use another compiler at some point in time ? Option 4 only works if you only use VS and gcc.
Notice that option 1 may make gcc compilation suffer a few seconds. Although it may not be noticeable.
It's simple, really:
Project->Project Settings (Alt + F7)
Project-Settings-Dialog:
C++ -> Category: Precompiled Headers -> Precompiled Headers radio buttons --> disable
Since stdafx.h is by default all the Windows-specific stuff, I've put an empty stdafx.h on my other platform. That way your source code stays identical, while effectively disabling stdafx on Linux without having to remove all the #include "stdafx.h" lines from your code.
If you are using CMake in your project, then there are modules which automate it for you, very convenient, for example see cmake-precompiled-header here. To use it just include the module and call:
include( cmake-precompiled-header/PrecompiledHeader.cmake )
add_precompiled_header( ${target} ${header} FORCEINCLUDE SOURCE_CXX ${source} )
Another module called Cotire creates the header file to be precompiled (no need to manually write StdAfx.h) and speeds up builds in other ways - see here.
I've done both option 2 (#ifdef) and option 4 (PCH for gcc) for cross platform code with no issues.
I find gcc compiles much faster than VS so the precompiled headers are generally not that important, unless you are referencing some huge header file.
I have a situation where #2 in particular didn't work for me (There are numerous VS build configs where a #ifdef around #include "stdafx.h" does not work). Other solutions were suboptimal because the files themselves were cross-project as well as being cross-platform. I did not want to force preprocessor macros to be set or force linux or even windows builds to use (or not use) pch, so...
What I did, given a file named notificationEngine.cpp, for example, was removed the #include stdafx.h line entirely, created a new file in the same directory called pchNotificationEngine.cpp with the following contents:
#include "stdafx.h"
#include "notificationEngine.cpp"
Any given project can just include the correct version of the file. This admittedly is probably not the best option for cpp files that are only used by a single project.