CODEWITHSUNDEEP
makefilegnu-make
Meph
Meph

Reputation: 372

What are LINK.cpp / COMPILE.cpp Variables good for in make?

Shortly before I asked this question : g++ undefined reference to library symbols

It seems I misused predefined variables of make, namely LINK.cpp. The error was that I linked the library before the objects instead of afterwards.

Now this raised the question what those variables, particularly the LINK.cpp one, are good for because they expand like this :

LINK.cpp = $(LINK.cc)
LINK.cc = $(CXX) $(CXXFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH)
                                          ^

I usually store my libs in LDFLAGS variable, which I thought was common, so LINK.cc will always link the libs before , because I can add my object files only after, and will cause errors like in the posted question.

Where do I have to put my objects then to use the LINK.cpp variable properly? Candidates are :

,which both seem not to be right. Have I gotten the use case of the variable wrong ?

To be clear : The question does not aim at the errors a linker can throw at you, but the usage of the variables in make.

Upvotes: 2

Views: 786

Answers (1)

Mike Kinghan
Mike Kinghan

Reputation: 61575

I usually store my libs in LDFLAGS variable, which I thought was common

It is a fairly common mistake. The conventional meanings of the make variables that figure in C or C++ compilation are:-

  • CFLAGS: Compilation options for C
  • CXXFLAGS: Compilation options for C++
  • CPPFLAGS: Preprocessor options for C or C++
  • LDFLAGS: Linkage options, excluding library (-l) options
  • LDLIBS: Libraries or library (-l) options for linkage.

These are the meanings assumed in GNU Make's builtin rules.

The intended use of the variable:

LINK.cc = $(CXX) $(CXXFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH)

is therefore as in:

prog: $(OBJS)
    $(LINK.cc) $^ $(LDLIBS) -o $@

with the libraries following the object files.

(The variable TARGET_ARCH appears in builtin rules evidently with the intended meaning target-architecture options, but is nontheless undocumented).

Upvotes: 4

Related Questions