flex与bison学习之简易计算器

第1章例子-简易计算器

简易计算器

代码(001_5_simple_calculator.y)

/* 简易计算器 */
%{
#include<stdio.h>
%}/* 定义记号 */
%token NUMBER
%token ADD SUB MUL DIV ABS
%token EOL
%%calclist: /* 空规则 */| calclist exp EOL { printf("=%d\n", $2); } /* 从输入开头开始匹配 */;exp: factor| exp ADD factor { $$ = $1 + $3; }| exp SUB factor { $$ = $1 - $3; };factor: term| factor MUL term { $$ = $1 * $3; }| factor DIV term { $$ = $1 / $3; };term: NUMBER| ABS term { $$ = $2 >= 0 ? $2 : -$2; };
%%main(int argc, char **argv)
{yyparse();
}yyerror(char *s)
{fprintf(stderr, "error: %s\n", s);
}

代码(001_5_simple_calculator.l)

/* 简易计算器 */
%{
#include"001_5_simple_calculator.tab.h"
%}%%
"+"         { printf("%s", yytext); return ADD; }
"-"         { printf("%s", yytext); return SUB; }
"*"         { printf("%s", yytext); return MUL; }
"/"         { printf("%s", yytext); return DIV; }
"|"         { printf("%s", yytext); return ABS; }
[0-9]+      { yylval = atoi(yytext); printf("%s", yytext); return NUMBER; }
\n          { return EOL; }
[ \t]       { /* 忽略空白字符 */ }
.           { printf("Mystery character %c\n", *yytext); }%%

Makefile(001_5_simple_calculator.Makefile)

FILE_NAME = $(file_name)BISON_INPUT_FILE = $(FILE_NAME).y
BISON_OUTPUT_SRC_FILE = $(FILE_NAME).tab.c
BISON_OUTPUT_HEADER_FILE = $(FILE_NAME).tab.h
BISON_OBJECT_FILE = $(FILE_NAME).tab.o
BISON_CMD = bison
BISON_OUTPUT_FLAG = -o
BISON_DEFINE_FLAG = -dFLEX_INPUT_FILE = $(FILE_NAME).l
FLEX_OUTPUT_FILE = $(FILE_NAME).c
FLEX_CMD = flex
FLEX_FLAG = -oGCC_CMD = gcc
GCC_COMPILE_FLAG = -c
GCC_OUTPUT_FLAG = -o
GCC_LINK_FLAG = -lfl
GCC_OBJECT_FILE = $(FILE_NAME).oTARGET_FILE = $(FILE_NAME)all: clean bison_main flex_main gcc_mainbison_main: $(BISON_INPUT_FILE)$(BISON_CMD) $(BISON_OUTPUT_FLAG) $(BISON_OUTPUT_SRC_FILE) $(BISON_DEFINE_FLAG) $(BISON_INPUT_FILE)flex_main: $(FLEX_INPUT_FILE) $(BISON_OUTPUT_HEADER_FILE)$(FLEX_CMD) $(FLEX_FLAG) $(FLEX_OUTPUT_FILE) $(FLEX_INPUT_FILE)gcc_main: $(FLEX_OUTPUT_FILE)$(GCC_CMD) $(GCC_COMPILE_FLAG) $(BISON_OUTPUT_SRC_FILE) $(GCC_OUTPUT_FLAG) $(BISON_OBJECT_FILE)$(GCC_CMD) $(GCC_COMPILE_FLAG) $(FLEX_OUTPUT_FILE) $(GCC_OUTPUT_FLAG) $(GCC_OBJECT_FILE)$(GCC_CMD) $(BISON_OBJECT_FILE) $(GCC_OBJECT_FILE) $(GCC_LINK_FLAG) $(GCC_OUTPUT_FLAG) $(TARGET_FILE).PHONY: cleanclean:@rm -f $(BISON_OUTPUT_SRC_FILE)@rm -f $(BISON_OUTPUT_HEADER_FILE)@rm -f $(BISON_OBJECT_FILE)@rm -f $(FLEX_OUTPUT_FILE)@rm -f $(GCC_OBJECT_FILE)@rm -f $(TARGET_FILE)

编译指令

make -f 001_5_simple_calculator.Makefile file_name=001_5_simple_calculator

测试指令

./001_5_simple_calculator
#输入以下信息，按Ctrl+D结束
2 + 3 * 4
2 * 3 + 4
20 / 4 - 2
20 - 4 / 2

输出信息

---

进阶计算器

增加对小括号以及注释的支持

代码(001_5_simple_calculator_plus.y)

/* 简易计算器 */
%{
#include<stdio.h>
%}/* 定义记号 */
%token NUMBER
%token ADD SUB MUL DIV ABS
%token OP CP
%token EOL
%%calclist: /* 空规则 */| calclist exp EOL { printf("=%d\n> ", $2); }| calclist EOL     { printf("> "); } /* 空行或注释 */;exp: factor| exp ADD exp    { $$ = $1 + $3; }| exp SUB factor { $$ = $1 - $3; }| exp ABS factor { $$ = $1 | $3; };factor: term| factor MUL term { $$ = $1 * $3; }| factor DIV term { $$ = $1 / $3; };term: NUMBER| ABS term  { $$ = $2 >= 0 ? $2 : -$2; }| OP exp CP { $$ = $2; };
%%main(int argc, char **argv)
{printf("> ");yyparse();
}yyerror(char *s)
{fprintf(stderr, "error: %s\n", s);
}

代码(001_5_simple_calculator_plus.l)

/* 简易计算器 */
%{
#include"001_5_simple_calculator_plus.tab.h"
%}%%
"+"         { printf("%s", yytext); return ADD; }
"-"         { printf("%s", yytext); return SUB; }
"*"         { printf("%s", yytext); return MUL; }
"/"         { printf("%s", yytext); return DIV; }
"|"         { printf("%s", yytext); return ABS; }
"("         { printf("%s", yytext); return OP; }
")"         { printf("%s", yytext); return CP; }
[0-9]+      { yylval = atoi(yytext); printf("%s", yytext); return NUMBER; }
\n          { return EOL; }
"//".*      { printf("original characters is: %s\n", yytext); }
[ \t]       { /* 忽略空白字符 */ }
.           { printf("Mystery character %c\n", *yytext); }%%

编译指令

make -f 001_5_simple_calculator.Makefile file_name=001_5_simple_calculator_plus

测试指令

./001_5_simple_calculator_plus
#输入以下信息，按Ctrl+D结束
1 + 2 * ( 3 + 4 )
9 / ( 10 - 7 )

输出信息