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POHow to pass a value to Make, which gets passed to C code
 

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    <p>I'm looking for help getting my Makefile to do what I want it to do.</p> <p>I have figured out how to add preprocessing code to my C source which will compile only if I'm compiling for debug:</p> <pre><code>#if DEBUG printf("main()\n"); { /* Pauses execution so gdb can attach. */ int i=9; pid_t PID; char hostname[256]; gethostname(hostname, sizeof(hostname)); printf("PID %d on %s ready for attach.\n", PID=getpid(), hostname); fflush(stdout); while (i&gt;0) { sleep(5); i--; } } #endif </code></pre> <p>And I've figured out that if I add <code>-DDEBUG=1</code> to my compile statement, that the above code will be compiled (otherwise it's not compiled).</p> <p>Next, I want to pass a flag to my Makefile which will either include, or not include the <code>-D</code> option. Currently, I have two separate compile lines which I comment and uncomment as appropriate. Here is my Makefile (which I inherited from someone and am having a difficult time understanding). See the lines that say <code>CFLAGS</code>?:</p> <pre><code>SHELL = /bin/sh prefix = /home/schwarz/sundials/instdir exec_prefix = ${prefix} includedir = ${prefix}/include libdir = ${exec_prefix}/lib CPP = cc -E CPPFLAGS = CC = cc # CFLAGS = -Wall -g CFLAGS = -Wall -g -DDEBUG=1 # CFLAGS = -g -O2 LDFLAGS = LIBS = -lm MPICC = /usr/local/mpi/bin/mpicc MPI_INC_DIR = /usr/local/mpi/bin/../include MPI_LIB_DIR = /usr/local/mpi/bin/../lib MPI_LIBS = MPI_FLAGS = INCLUDES = -I${includedir} -I${MPI_INC_DIR} LIBRARIES = -lsundials_cvode -lsundials_nvecparallel ${LIBS} LIBRARIES_BL = EXAMPLES = FPU # cvAdvDiff_non_p cvDiurnal_kry_bbd_p cvDiurnal_kry_p OBJECTS = ${EXAMPLES:=.o} # ----------------------------------------------------------------------------------------- .SUFFIXES : .o .c .c.o : ${MPICC} ${CPPFLAGS} ${CFLAGS} ${MPI_FLAGS} ${INCLUDES} -c $&lt; # ----------------------------------------------------------------------------------------- all: ${OBJECTS} @for i in ${EXAMPLES} ; do \ echo "${MPICC} -o $${i} $${i}.o ${MPI_FLAGS} ${CFLAGS} ${LDFLAGS} -L${libdir} ${LIBRARIES} -L${MPI_LIB_DIR} ${MPI_LIBS} ${LIBRARIES_BL}" ; \ ${MPICC} -o $${i} $${i}.o ${MPI_FLAGS} ${CFLAGS} ${LDFLAGS} -L${libdir} ${LIBRARIES} -L${MPI_LIB_DIR} ${MPI_LIBS} ${LIBRARIES_BL}; \ done clean: rm -f ${OBJECTS} rm -f ${EXAMPLES} </code></pre> <p>I have searched the web - I swear! - but cannot figure out how to pass a parameter into the makefile. <em>How can I set up my Makefile so that it does different types of compiles of the same code for different compile needs?</em> Even better would be if I could pass a specific value to the Makefile, which would pass a specific value to the compile, which I could use to initialize <code>i</code> in the code. (IOW, I compile as <code>make 8</code> and the C is compiled as <code>int i=8;</code>). Is any of that even possible in Make?</p> <p>As an aside, I've read about Makefiles and how they work by listing files with labels (colons), followed by their dependencies. But I can't understand how this Makefile works or why it issues two compile statements. So a brief explanation would also be helpful.</p>
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    1. COHave you read [this section](http://sunsite.ualberta.ca/Documentation/Gnu/make-3.79/html_chapter/make_7.html) of the manual? Also, don't use `=` and prefer `:=` whenever possible.
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    2. CO@KerrekSB Good link, though not many examples. I still needed how to pass values into make. Thanks.
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