Question

I’m using a header only library and would like to include only the part of the library that I’m actually using.

If I include one of the library’s headers how can I find all the other headers that are included by the library? Or phrased more generally: how can I find all files that make up a C++ translation unit? (I’m using g++ on Linux.)

Edit: Possible approaches with gcc (answers summary)

• gcc -H produces output of the form:

  ... /usr/include/c++/4.6/cmath
  .... /usr/include/math.h
  ..... /usr/include/x86_64-linux-gnu/bits/huge_val.h
  ..... /usr/include/x86_64-linux-gnu/bits/huge_valf.h
  

  You have to filter out the system headers manually, though.

• gcc -E gives you the raw preprocessor output:

  # 390 "/usr/include/features.h" 2 3 4
  # 38 "/usr/include/assert.h" 2 3 4
  # 68 "/usr/include/assert.h" 3 4
  extern "C" {    
  extern void __assert_fail (__const char *__assertion, __const char *__file,
        unsigned int __line, __const char *__function)
        throw () __attribute__ ((__noreturn__));
  

  You have to parse the linemarkers manually. See: http://gcc.gnu.org/onlinedocs/cpp/Preprocessor-Output.html

• gcc -M produces a Make file for the given source file. The output looks as follows:

  object.o: mylibrary/object.h /usr/include/c++/4.6/map \
   /usr/include/c++/4.6/bits/stl_tree.h \
   /usr/include/c++/4.6/bits/stl_algobase.h \
   /usr/include/c++/4.6/x86_64-linux-gnu/./bits/c++config.h \
  

Answer 1

I believe you’re looking for gcc -H.