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Asked: 2026-06-08T08:53:56+00:00

I cannot explain the behaviour I am seeing when linking my code. Maybe someone

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I cannot explain the behaviour I am seeing when linking my code. Maybe someone has an idea what’s going on…

I have a multiple file C++ project which uses GNU automake tools as its build system (all on Linux).

After adding a source and header file (lets call them util.cc and util.h) to the project and having an already existing source file (calc.cc) calling a function from the newly added files I get a linking error depending on where the include statement appears. I repeat: The error occurs in the linking step, compilation runs fine!!

Example:

I get an error when putting the new include statement at the end of the preexisting statements, like:

calc.cc:

#include "file1.h"
#include "file2.h"
#include "file3.h"
#include "file4.h"
#include "util.h"   // new header

This version compiles fine. But linking produces an error (symbol not found)!!

Now, when changing this to

#include "util.h"   // new header
#include "file1.h"
#include "file2.h"
#include "file3.h"
#include "file4.h"

then compilation and linking runs fine!

Since the linker only reads the .o files, this must mean that different content is produced depending on where the include statement appears. How can this be?

Compiler is g++ (GCC) 4.4.6

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1 Answer

  1. Editorial Team

    Chances are that util.h has a #define that changes the behaviour of one of the other files.

    Your best chance of working out exactly what is going on would involve examining those header files for the name of the missing symbol and getting the pre-processor output from compiling calc.cc both ‘working’ and ‘non working’ way, and comparing the two files.

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