flex与bison学习之识别计算器的记号

第1章例子-识别计算器的记号

识别计算器的记号

代码(001_4_calculator_tokens.l)

/* 识别出用于计算器的记号并把他们输出 */
%{enum yytokentype {NUMBER = 258,ADD = 259,SUB = 260,MUL = 261,DIV = 262,ABS = 263,EOL = 264 /* 行尾结束符 */};int yylval;
%}%%
"+"         { return ADD; }
"-"         { return SUB; }
"*"         { return MUL; }
"/"         { return DIV; }
"|"         { return ABS; }
[0-9]+      { yylval = atoi(yytext); return NUMBER; }
\n          { return EOL; }
[ \t]       { /* 忽略空白字符 */ }
.           { printf("Mystery character %c\n", *yytext); }%%
main (int argc, char **argv)
{int tok;while (tok = yylex()) {printf("%d", tok);if (tok == NUMBER) {printf(" = %d\n", yylval);} else {printf("\n");} }
}

Makefile(model.Makefile)

FILE_NAME = $(file_name)FLEX_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 flex_main gcc_mainflex_main: $(FLEX_INPUT_FILE)$(FLEX_CMD) $(FLEX_FLAG) $(FLEX_OUTPUT_FILE) $(FLEX_INPUT_FILE)gcc_main: $(FLEX_OUTPUT_FILE)$(GCC_CMD) $(GCC_COMPILE_FLAG) $(FLEX_OUTPUT_FILE) $(GCC_OUTPUT_FLAG) $(GCC_OBJECT_FILE)$(GCC_CMD) $(GCC_OBJECT_FILE) $(GCC_LINK_FLAG) $(GCC_OUTPUT_FLAG) $(TARGET_FILE).PHONY: cleanclean:@rm -f $(FLEX_OUTPUT_FILE)@rm -f $(GCC_OBJECT_FILE)@rm -f $(TARGET_FILE)

编译指令

make -f model.Makefile file_name=001_4_calculator_tokens

测试指令

./001_4_calculator_tokens
#输入以下信息，按Ctrl+D结束
a / 34 + |45

输出信息