CODEWITHSUNDEEP
g++makefile
mahmood
mahmood

Reputation: 24705

make output is different from Makefile

I have a Makefile with this content

$ cat Makefile
all: locality
locality: src/locality.o
    g++ src/locality.o -o locality

locality.o: src/locality.cpp
    g++ -O3  -c src/locality.cpp

clean:
    rm -rf src/*.o locality

However when I run make, I see some slightly different output!

$ make clean
rm -rf src/*.o locality

$ make
g++    -c -o src/locality.o src/locality.cpp
g++ src/locality.o -o locality

So where is -O3??

Upvotes: 0

Views: 46

Answers (2)

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798676

You tripped over a built-in rule in GNU make, namely %.o: %.c. Use $CFLAGS instead.

CFLAGS=-O3

all: locality
locality: src/locality.o
    g++ src/locality.o -o locality

clean:
    rm -rf src/*.o locality

Upvotes: 2

Jens
Jens

Reputation: 72649

Make is using an implicit rule to create src/locality.o because you have no rule for it (you only have a rule for locality.o in the current directory, not in src.

This is what you get for violating one of Paul's rules of Makefiles:

Every non-.PHONY rule must update a file with the exact name of its target.

To do that, you should use $@ in your rule to designate the target file.

Upvotes: 1

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