makefile for a yacc and flex [closed] - c

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I have a make-based project involving yacc and lex, but make is performing actions that I do not expect and cannot explain from my makefile:
a.out: lex.yy.o y.tab.o ass3_14CS101.o
gcc lex.yy.o y.tab.o ass3_14CS101.o -lfl
ass3_14CS101.o: ass3_14CS101.c
gcc -c ass3_14CS101.c
lex.yy.o: lex.yy.c
gcc -c lex.yy.c
y.tab.o: y.tab.c
gcc -c y.tab.c
lex.yy.c: ass3_14CS101.l y.tab.h
flex ass3_14CS101.l
y.tab.c: ass3_14CS101.y
yacc -dtv ass3_14CS101.y -W
y.tab.h: ass3_14CS101.y
yacc -dtv ass3_14CS101.y -W
clean:
rm lex.yy.c y.tab.c y.tab.h lex.yy.o y.tab.o ass3_14CS101.o y.output a.out
test:
./a.out < ass3_14CS101_test.c
Here is the output of one make run:
yacc -dtv ass3_14CS10061.y -W
ass3_14CS10061.y:48.10: warning: empty rule without %empty [-Wempty-rule]
statement : ;
^
flex ass3_14CS10061.l
ass3_14CS10061.l:77: warning, rule cannot be matched
gcc -c lex.yy.c
gcc -c y.tab.c
yacc ass3_14CS10061.y
mv -f y.tab.c ass3_14CS10061.c
gcc -c ass3_14CS10061.c
gcc lex.yy.o y.tab.o ass3_14CS10061.o -lfl
ass3_14CS10061.o: In function `yyparse':
ass3_14CS10061.c:(.text+0x20): multiple definition of `yyparse'
y.tab.o:y.tab.c:(.text+0x289): first defined here
ass3_14CS10061.o: In function `yyerror':
ass3_14CS10061.c:(.text+0x7f6): multiple definition of `yyerror'
y.tab.o:y.tab.c:(.text+0xd61): first defined here
collect2: error: ld returned 1 exit status
make: *** [a.out] Error 1
Where did the mv -f command (the bold line above) come from? There is no such command in the Makefile, and it is causing the build to fail.

Answer 1

You have:
a.out: lex.yy.o y.tab.o ass3_14CS101.o
gcc lex.yy.o y.tab.o ass3_14CS101.o -lfl
ass3_14CS101.o: ass3_14CS101.c
gcc -c ass3_14CS101.c
The first rule says the compilation needs to ensure ass3_14CS101.o is up to date. The second rule says you create ass3_14CS101.o by compiling ass3_14CS101.c. None of the other specified rules say anything about how to create ass3_14CS101.c, but make is clever.
Given that there's a file ass3_14CS101.y, make knows how to create ass3_14CS101.c from it: it runs yacc and moves yy.tab.c to ass3_14CS101.c. So, that's what you see it doing.
You might note that make is running the yacc command again before the mv you noted; and that invocation is different from the first.
You need to use more macros. YACC contains the name of the Yacc-like program, and YFLAGS conventionally contains the arguments to it (it looks like you prefer -dtv -W as the Yacc flags). Similarly with the C compiler (CC and CFLAGS) and linking often adds LDFLAGS and LDLIBS — so you end up with a command line like:
${CC} -o $# ${CFLAGS} ${OBJECTFILES} ${LDFLAGS} ${LDLIBS}
as the linking command line. The macro I designated as ${OBJECTFILES} is a list of the object files that should be linked. Note that ${CFLAGS} is included; it often contains the -g option for debug information, and you need that in the link command line as well as the object file command lines.
One major benefit of using macros is that you can adjust the compilation from the make command line if need so be — without editing the makefile.