Question

I am trying to compile my program which has a lex file and a yacc file and a couple of C files.I came across this example in the Flex manual.

I have a couple of questions regarding this makefile.It doesn't specify a compiler such as gcc how does the makefile know how to create the targets such as scan.o and parse.o and 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

这是一个Makefile功能：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

在您的情况下，相关部分是

编译C程序

n.o是从n.c自动生成的，其形式为'$（CC）$（CPPFLAGS）$（CFLAGS）-c'。

[...]

Yacc for C program
     通过使用配方'$（YACC）$（YFLAGS）'运行Yacc，从n.y自动生成
。

Lex for C program

n.c是通过运行Lex从n.l自动生成的。实际配方是'$（LEX）$（LFLAGS）'。

根据https://ftp.gnu.org/old-gnu/Manuals/make-3.79.1/html_chapter/make_12.html，一些规则不可移植......

simple makefile for lex yacc and C

1 个答案: