Make不喜欢$(addprefix a,b)

Make给了我一个错误:

make/sources.make:16: *** missing separator.  Stop.
The terminal process terminated with exit code: 2

生成此错误的代码是:

$(addprefix a,b)

我查过车位,但什么也没找到。 如果我把它注释掉,就不会出错。我把范围缩小到这一行,我想不出来。”“a”和“b”可以用任何东西代替,但仍然不起作用。但是,如果删除所有参数,如下所示 $(addprefix ,) 然后没有错误。

这是怎么回事?

包含错误的makefile的完整代码:

# sources.make - source files

# path of source files
SOURCEPATH=src

# build list of source files
# categorize source files

SOURCE_MAIN=main.c

# add categories to SOURCES as needed
SOURCES+=$(SOURCE_MAIN)

# add the SOURCEPATH to each source file
#$(addprefix $(SOURCEPATH),$(SOURCES)) <------ This is the true error code
$(addprefix a,b)

# extra files to remove
TRASHFILES = stdout.txt stderr.txt

# extra directories to remove
TRASHDIRS = junkdir

# build target
TARGET = $(PROG)$(EXT)

# generate object files
OBJECTS = $(patsubst %.c,%.o,$(SOURCES))

# generate dependency files
DEPENDS = $(patsubst %.c,%.d,$(SOURCES))