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1. How the system works

The build counter system presented in this article can be used to keep track of how many times your linker is invoked when you build your executables. The system is comprised of two pieces of code, one m4 source file and some code that goes into your Makefile after the linker is invoked. Suppose your executable is called 2010/tests/hello.exe. Then the name of the file that keeps track of how many times the linker is invoked is called 2010/tests/hello.num where the .num file extension stands for number. The system is robust enough to handle cases where the file 2010/tests/hello.num does not exist as will be the case when the linker is run for the first time with the extra linker code. The reason that the number of linker invocations is counted is that linking is always done once at the end of a series of compilations.

2. How to install the system

The following m4 code can be used to keep track to the build counts of your linker:

m4_define(COUNTER,m4_eval(m4_sinclude(FILE) + 1))m4_dnl
m4_esyscmd(echo >FILE COUNTER)m4_dnl
*** Updated build count to new value: COUNTER

Place the above code into a file called build-counter.txt and add the following code to your Makefile's linker call:

m4 -P -DFILE=$*.num build-counter.txt

so that the command to invoke the linker looks something like what follows:

%.exe: %.o $(LINK_WITH)
        @printf "** Linking %s %s\n" $*.exe $(INFO_OPTION)
        g++ $^ -o $*.exe $(LDFLAGS)
        m4 -P -DFILE=$*.num build-counter.txt

3. How to use the system

If /path/to/X.num is the name of your *.num file, then you can use m4 to include it in other documents using the command m4_include(/path/to/X.num), or you can issue the command cat /path/to/X.num to print out the value of the number stored in the file like so in your Makefile:

@echo "The current value for build count is: " $$(cat /path/to/X.num)

4. How to customise GNU Emacs to hide *.num files

By altering the variable dired-omit-extensions and completion-ignored-extensions you can hide the *.num files from being visible in Emacs' directory editor, dired and from showing up using TAB file completion. Here are the values for dired-omit-extensions and completion-ignored-extensions that work for my version of Emacs:

(setq dired-omit-extensions
   (append
      (list
         ".num")
         dired-omit-extensions))

(setq completion-ignored-extensions
   (append
      (list
         ".num")
         completion-ignored-extensions))