GNU Makefile，C编程

Question

my current makefile looks likes this

all: hello

hello: hello.o
    clang -o hello hello.o

hello.o: hello.c
    clang -Wall -std=c99 -c -o hello.o hello.c -lpthread

clean:
rm -f *.o *exe hello

---

How can I modify it to compile with the following:

clang -std=gnu99 -Wall -o hello hello.c -lpthread

Answer 1

Use

hello: hello.c
    clang -std=gnu99 -Wall -o hello hello.c -lpthread

instead of the two rules you have for hello and hello.o now.

When your program gets bigger, however, the separation of compilation to object files and linking may at some point be faster than compiling and linking everything in one go. With separated compilation and linking compilation units that are unmodified do not need to be recompiled every time.

Answer 2

Try this - usually best to do the compiling is a few steps.

all: hello

hello: hello.o
    clang -o hello hello.o -lpthread

hello.o: hello.c
    clang -Wall -std=c99 -c -o hello.o hello.c 

clean:
rm -f *.o  hello

Answer 3

Your modification requires just changing a single line; but instead, you should use some variables to make it cleaner:

# C compiler
CC = clang
# Additional libraries
LIBS = -lpthread
# Compiler flags
CCFLAGS = -std=gnu99 -Wall $(LIBS)
# Output executable
OUT = hello

all: hello

hello: hello.o
    $(CC) $(CCFLAGS) -o $(OUT) hello.o

hello.o: hello.c
    clang $(CCFLAGS) -c -o hello.o hello.c

clean:
    rm -f *.o $(OUT)