第1章例子-简易计算器(C语言实现词法分析)
flowchart LR
A([根节点])
A-->B[分支1]
A-->C[分支2]
A-->D[分支3]
A-->E[分支4]
A-->F[分支5]
简易计算器(C语言实现词法分析)
代码(001_6_simple_calculator_in_c.c)
// 用于计算器的词法分析器的手写版本
#include<stdio.h>
#include"001_6_simple_calculator_in_c.tab.h"FILE *yyin;
static int seeneof = 0;int yylex(void) {if (!yyin) {yyin = stdin;}if (seeneof) {return 0; // 上次读到的是EOF}while (1) {int c = getc(yyin);// 处理数字并获取其整数值if (isdigit(c)) {int i = c - '0';while (isdigit(c = getc(yyin))) {i = (10 * 1) + c - '0';}yylval = i;if (c == EOF) {seeneof = 1;} else {ungetc(c, yyin);}printf("%d", i);return NUMBER;}// 处理各种数学运算符switch (c) {case '+': {printf("+");return ADD;}case '-': {printf("-");return SUB;}case '*': {printf("*");return MUL;}case '|': {printf("|");return ABS;}case '(': {printf("(");return OP;}case ')': {printf(")");return CP;}case '\n': {return EOL;}case ' ':case '\t':break; // 忽略空格和水平制表符case EOF: {return 0; // 标准的文件结束符}case '/': {c = getc(yyin);if (c == '/') { // 这是注释printf("original characters is: //");while ((c = getc(yyin)) != '\n') {if (c == EOF) {return 0; // EOF出现在注释行里}printf("%c", c);}printf("%c> ", c);break;}// 这是除法操作符printf("/");if (c == EOF) {seeneof = 1; } else {ungetc(c, yyin);}return DIV;}default: {yyerror("Mystery character %c\n", c);break;}}}
}代码(001_6_simple_calculator_in_c.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);
}Makefile(001_6_simple_calculator_in_c.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 = -dC_SRC_FILE = $(FILE_NAME).cGCC_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 gcc_mainbison_main: $(BISON_INPUT_FILE)$(BISON_CMD) $(BISON_OUTPUT_FLAG) $(BISON_OUTPUT_SRC_FILE) $(BISON_DEFINE_FLAG) $(BISON_INPUT_FILE)gcc_main: $(FLEX_OUTPUT_FILE) $(BISON_OUTPUT_HEADER_FILE) $(C_SRC_FILE)$(GCC_CMD) $(GCC_COMPILE_FLAG) $(BISON_OUTPUT_SRC_FILE) $(GCC_OUTPUT_FLAG) $(BISON_OBJECT_FILE)$(GCC_CMD) $(GCC_COMPILE_FLAG) $(C_SRC_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 $(GCC_OBJECT_FILE)@rm -f $(TARGET_FILE)编译指令
make -f 001_6_simple_calculator_in_c.Makefile file_name=001_6_simple_calculator_in_c
测试指令
./001_6_simple_calculator_in_c
#输入以下信息，按Ctrl+D结束
1 + 2 * ( 3 + 4 )
9 / ( 10 - 7 )
// this is a comment line
输出信息
