codeblocks-ep/help/html/programmerHelp/make/Eval-Function.html at master · maifeeulasad/codeblocks-ep · GitHub

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Node:<a name="Eval%20Function">Eval Function</a>,
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<h3 class="section">The <code>eval</code> Function</h3>

   <p>The <code>eval</code> function is very special: it allows you to define new
makefile constructs that are not constant; which are the result of
evaluating other variables and functions.  The argument to the
<code>eval</code> function is expanded, then the results of that expansion
are parsed as makefile syntax.  The expanded results can define new
<code>make</code> variables, targets, implicit or explicit rules, etc.

   <p>The result of the <code>eval</code> function is always the empty string;
thus, it can be placed virtually anywhere in a makefile without
causing syntax errors.

   <p>It's important to realize that the <code>eval</code> argument is expanded
<em>twice</em>; first by the <code>eval</code> function, then the results of
that expansion are expanded again when they are parsed as makefile
syntax.  This means you may need to provide extra levels of escaping
for "$" characters when using <code>eval</code>.  The <code>value</code>
function (see <a href="Value-Function.html#Value%20Function">Value Function</a>) can sometimes be useful in these
situations, to circumvent unwanted expansions.

   <p>Here is an example of how <code>eval</code> can be used; this example
combines a number of concepts and other functions.  Although it might
seem overly complex to use <code>eval</code> in this example, rather than
just writing out the rules, consider two things: first, the template
definition (in <code>PROGRAM_template</code>) could need to be much more
complex than it is here; and second, you might put the complex,
"generic" part of this example into another makefile, then include
it in all the individual makefiles.  Now your individual makefiles are
quite straightforward.

<pre class="example">     PROGRAMS    = server client

     server_OBJS = server.o server_priv.o server_access.o
     server_LIBS = priv protocol

     client_OBJS = client.o client_api.o client_mem.o
     client_LIBS = protocol

     # Everything after this is generic

     .PHONY: all
     all: $(PROGRAMS)

     define PROGRAM_template
      $(1): $$($(1)_OBJ) $$($(1)_LIBS:%=-l%)
      ALL_OBJS   += $$($(1)_OBJS)
     endef

     $(foreach prog,$(PROGRAMS),$(eval $(call PROGRAM_template,$(prog))))

     $(PROGRAMS):
             $(LINK.o) $^ $(LDLIBS) -o $@

     clean:
             rm -f $(ALL_OBJS) $(PROGRAMS)
     </pre>

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