CODEWITHSUNDEEP
cgcchyperlinkheadercompilation
slowmo
slowmo

Reputation: 81

Compile and link .h header files which many .c source programs use

I work for a group in which our test bucket has hundreds of .c source programs. The .c programs are fairly small and they all include the same 10 .h header files. These .h files are fairly large.

Each time we get a new library file to link our test programs to test, we run a script to recompile and run our test bucket against. The problem is that the compiling takes fairly long, especially if the environment is virtual.

Is there a way to compile the .h header files once, put in a separate object file and have those many .c source files link to said object file? I think this will speed up compiling time. I am willing to change/remove all the #include in the .c source programs.

Any suggestions to speeding up compile time is greatly appreciated.

Also, I should say that a script executes a makefile PER .c source test program! The makefile is not told to compile all programs in the current directory. Each test program is compiled into its own executable.

Upvotes: 1

Views: 1132

Answers (4)

millinon
millinon

Reputation: 1576

If I understand correctly, the way libraries typically work is by using precompiled code in object files ( .so on Linux systems? ), while providing header files ( .h ) for use in projects.

What happens is when you compile, the #include <library.h> directive finds that header and pastes its contents in the source file being compiled. Then, once the source file is compiled, it is linked to the precompiled object file. That way, the library can be included in a huge number of projects without it needing to be compiled from source each time. The only part that must be recompiled when linking to a library is the ( relatively ) small amount of code in the headers, which essentially makes library functions and variables accessible to the source code.

All this means is that to drastically speed up compilation, your best bet is to take all of the functions out of the 10 .h files, and instead leave only the function prototypes in the headers. Once you have all of the functions in separate .c source files, you can compile them into an object file ( typically -c flag ). Then, whenever you need to compile a new program against the 10 headers you typically use, you can instead include your stripped down version of the headers, and link to the precompiled object. Since only the new code in the .c file has to be compiled, instead of all of the code in the headers, the process should be much faster.

Upvotes: 0

Xephon
Xephon

Reputation: 393

Rewrite your headers. Strip off all definition and leave in header. Strip off all implementation and put in new .c. Compile as library. Link with solution. Distribute library on runtime system.

Upvotes: 1

Raffaele Rossi
Raffaele Rossi

Reputation: 1109

You've asked further suggestions to speed up your compilation.

One way can be using ccache. Basically, ccache keeps a cache of the object files compiled so far and returns them (instead of re-compiling again over and over) when it recognises that the same source file is being compiled again.

Using it should be as simple as

  1. Install ccache
  2. Prefix your gcc/cc/g++ command with ccache

Upvotes: 1

Yong Tiger
Yong Tiger

Reputation: 121

You could use precompiled header feature. See http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html

Upvotes: 2

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