Question

Running: gcc version 4.2.1 (Apple Inc. build 5664)

I created an apple XCode project with a default precompiled header. It appears to be very slow, and a trivial main file with a main function no includes no code takes 6 seconds to compile, which is after I upgraded to a new SSD drive. I am on a laptop, but I have reservations that upgrading to a workstation would alleviate my problem. If I turn off the precompiled header then the main file compiles in under a second. It appears that using a precompiled header puts a penalty across all files. This delay is makes me want to avoid compiling and experimenting with code which is not good. Here is what I am including in my precompiled header:

#pragma once

#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <fstream>
#include <functional>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <valarray>
#include <vector>

#include <boost/smart_ptr/scoped_ptr.hpp>
#include <boost/smart_ptr/scoped_array.hpp>
#include <boost/smart_ptr/shared_ptr.hpp>
#include <boost/smart_ptr/shared_array.hpp>
#include <boost/smart_ptr/make_shared.hpp>  
#include <boost/smart_ptr/weak_ptr.hpp>
#include <boost/smart_ptr/intrusive_ptr.hpp>

#include <boost/regex.hpp>
#include <boost/thread.hpp>
#include <boost/bind/bind.hpp>
#include <boost/bind/apply.hpp>
#include <boost/bind/protect.hpp>
#include <boost/bind/make_adaptable.hpp>

#include <boost/asio.hpp>
//#include <boost/asio/ssl.hpp>


#include <boost/property_tree/ptree.hpp>
#include <boost/random.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/date_time/gregorian/gregorian.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/local_time/local_time.hpp>
#include <boost/date_time/time_zone_base.hpp>
#include <boost/circular_buffer.hpp>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics.hpp>

I have not included spirit, which really makes the compile time go up.

Was it helpful?

Solution

GCC's precompiled headers work in a very particular way. Only one precompiled header file can be used in any given source file. Use -H to show whether a given header file is using a precompiled version or not.

Moreover, you must compile the header file with the exact same compiler flags as the source file that uses it.

The typical way to set up a PCH environment is like this:

main.cpp:

#include "allheaders.hpp"

int main() { /* ... */ }

allheaders.hpp:

#include <algorithm>
// ... everything you need

Compilation:

g++ $CXXFLAGS allheaders.hpp                 # 1
g++ $CXXFLAGS -H -c -o main.o main.cpp       # 2
g++ $LDFLAGS -o myprogram main.o             # 3

After Step #1 you should end up with a file allheaders.hpp.gch, which should be pretty big. In Step #2 the -H flag should produce additional output that tells you that the precompiled header file is being used. Step #3 links the executable.

The idea is that Step #1 can potentially take a very long time, but Step #2 should become a lot faster.

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