c - lex yacc 和 C 的简单 makefile

Question

我正在尝试编译我的程序，它有一个 lex 文件、一个 yacc 文件和几个 C 文件。我在 the Flex manual 中遇到了这个例子。 .

我有几个关于这个 makefile 的问题。它没有指定编译器，例如 gcc makefile 如何知道如何创建目标，例如 scan.o和 parse.o和 myprogram.o ?

     # Makefile example -- scanner and parser.
     # Creates "myprogram" from "scan.l", "parse.y", and "myprogram.c"
     #
     LEX     = flex
     YACC    = bison -y
     YFLAGS  = -d
     objects = scan.o parse.o myprogram.o

     myprogram: $(objects)
     scan.o: scan.l parse.c
     parse.o: parse.y
     myprogram.o: myprogram.c

Answer 1

这是 Makefile 的一个特性:存在一些隐式规则并记录在 https://www.gnu.org/software/make/manual/html_node/Catalogue-of-Rules.html#Catalogue-of-Rules 中。
在你的情况下，相关部分是

Compiling C programs

n.o is made automatically from n.c with a recipe of the form ‘$(CC) $(CPPFLAGS) $(CFLAGS) -c’.

[...]

Yacc for C programs

n.c is made automatically from n.y by running Yacc with the recipe ‘$(YACC) $(YFLAGS)’.

Lex for C programs

n.c is made automatically from n.l by running Lex. The actual recipe is ‘$(LEX) $(LFLAGS)’.

根据 https://ftp.gnu.org/old-gnu/Manuals/make-3.79.1/html_chapter/make_12.html有些规则是不可移植的......