编译原理实验报告 词法分析器实验报告

设计思想 (1)程序主体结构部分： 说明部分 %% 规则部分 %% 辅助程序部分 （2）主体结构的说明 在这里说明部分告诉我们使用的LETTER,DIGIT, IDENT(标识符,通常定义为字母开头的字母数字串)和STR(字符串常量,通常定义为双引号括起来的一串字符)是什么意思.这部分也可以包含一些初始化代码.例如用#include来使用标准的头文件和前向说明(forward ，references).这些代码应该再标记"%{"和"%}"之间;规则部分&gt;可以包括任何你想用来分析的代码;我们这里包括了忽略所有注释中字符的功能,传送ID名称和字符串常量内容到主调函数和main函数的功能. （3）实现原理 程序中先判断这个句语句中每个单元为关键字、常数、运算符、界符，对与不同的单词符号给出不同编码形式的编码，用以区分之。 PL/0语言的EBNF表示 <常量定义>：：=<标识符>=<无符号整数>; <标识符>：：=<字母>={<字母>|<数字>}; <加法运算符>::=+|- <乘法运算符>::=*|/ <关系运算符>::==|#|<|<=|>|>= <字母>::=a|b|…|X|Y|Z <数字>::=0|1|2|…|8|9 三：设计过程 1． 关键字：void，main，if，then，break，int，Char，float，include，for，while，printfscanf 并为小写。 2．"+”;”-”;”*”;”/”;”:=“;”:”;”<“;”<=“;”>“;”>=“;”<>“;”=“;”(“;”)”;”;”;”#”为运算符。 3． 其他标记 如字符串，表示以字母开头的标识符。 4． 空格符跳过。 5． 各符号对应种别码 关键字分别对应1-13 运算符分别对应401-418，501-513。 字符串对应100 常量对应200 结束符# 四：举例说明 目标：实现对常量的判别 代码： digit [0-9] letter [A-Za-z] other_char [!-@\[-~] id ({letter}|[_])({letter}|{digit}|[_])* string {({letter}|{digit}|{other_char})+} int_num {digit}+ %% [ |\t|\n]+ "auto"|"double"|"int"|"struct"|"break"|"else"|"long"|"switch"|"case"|"enum"|"register"|"typedef"|"char"|"extern"|"return"|"union"|"const"|"float"|"short"|"unsigned"|"continue"|"for"|"signed"|"void"|"default"|"goto"|"sizeof"|"do"|"if"|"static"|"while"|"main" {Upper(yytext,yyleng);printf("%s,NULL\n",yytext);} \"([!-~])*\" {printf("CONST_string,%s\n",yytext);} -?{int_num}[.]{int_num}?([E][+|-]?{int_num})? {printf("CONST_real,%s\n",yytext);} "0x"?{int_num} {printf("CONST_int,%s\n",yytext);} ","|";"|"("|")"|"{"|"}"|"["|"]"|"->"|"."|"!"|"~"|"++"|"--"|"*"|"&"|"sizeof"|"/"|"%"|"+"|"-"|">"|"<"|">="|"<="|"=="|"!="|"&"|"^"|"|"|"&"|"||"|"+="|"-="|"*="|"/="|"%="|">>="|"<<="|"&="|"^="|"|="|"=" {printf("%s,NULL\n",yytext);} {id} {printf("ID,%s\n",yytext);} {digit}({letter})+ {printf("error1:%s\n",yytext);} %% #include <ctype.h> Upper(char *s,int l) { int i; for(i=0;i<l;i++) { s[i]=toupper(s[i]); } } yywrap() { return 1; } 五：DFA 六:数据测试 七：心得体会 其实匹配并不困难，主要是C++知识要求相对较高，只要把握住指针就好了。 附源程序： #include<iostream.h> #include<stdio.h> #include<stdlib.h> #include<string.h> int i,j,k,flag,number,status; /*status which is use to judge the string is keywords or not!*/ char ch; char words[10] = {" "}; char program[500]; int Scan(char program[]) { char *keywords[13] = {"void","main","if","then","break","int", "char","float","include","for","while","printf", "scanf"}; number = 0; status = 0; j = 0; ch = program[i++]; /* To handle the lettle space ands tab*/ /*handle letters*/ if ((ch >= 'a') && (ch <= 'z' )) { while ((ch >= 'a') && (ch <= 'z' )) { words[j++]=ch; ch=program[i++]; } i--; words[j++] = '\0'; for (k = 0; k < 13; k++) if (strcmp (words,keywords[k]) == 0) switch(k) { case 0:{ flag = 1; status = 1; break; } case 1:{ flag = 2; status = 1; break; } case 2:{ flag = 3; status = 1; break; } case 3:{ flag = 4; status = 1; break; } case 4:{ flag = 5; status = 1; break; } case 5:{ flag = 6; status = 1; break; } case 6:{ flag = 7; status = 1; break; } case 7:{ flag = 8; status = 1; break; } case 8:{ flag = 9; status = 1; break; } case 9:{ flag = 10; status = 1; break; } case 10:{ flag = 11; status = 1; break; } case 11:{ flag = 12; status = 1; break; } case 12:{ flag = 13; status = 1; break; } } if (status == 0) { flag = 100; } } /*handle digits*/ else if ((ch >= '0') && (ch <= '9')) { number = 0; while ((ch >= '0' ) && (ch <= '9' )) { number = number*10+(ch-'0'); ch = program[i++]; } flag = 200; i--; } /*opereation and edge handle*/ else switch (ch) { case '=':{ if (ch == '=') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 401; } else { i--; flag = 402; } break; } case'>':{ if (ch == '>') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 403; } else { i--; flag = 404; } break; } case'<':{ if (ch == '<') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 405; } else { i--; flag = 406; } break; } case'!':{ if (ch == '!') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 407; } else { i--; flag = 408; } break; } case'+':{ if (ch == '+') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 409; } else if (ch == '+') { words[j++] = ch; words[j] = '\0'; flag = 410; } else { i--; flag = 411; } break; } case'-':{ if (ch == '-') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 412; } else if( ch == '-') { words[j++] = ch; words[j] = '\0'; flag = 413; } else { i--; flag = 414; } break; } case'*':{ if (ch == '*') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 415; } else { i--; flag = 416; } break; } case'/':{ if (ch == '/') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 417; } else { i--; flag = 418; } break; } case';':{ words[j] = ch; words[j+1] = '\0'; flag = 501; break; } case'(':{ words[j] = ch; words[j+1] = '\0'; flag = 502; break; } case')':{ words[j] = ch; words[j+1] = '\0'; flag = 503; break; } case'[':{ words[j] = ch; words[j+1] = '\0'; flag = 504; break; } case']':{ words[j] = ch; words[j+1] = '\0'; flag = 505; break; } case'{':{ words[j] = ch; words[j+1] = '\0'; flag = 506; break; } case'}':{ words[j] = ch; words[j+1] = '\0'; flag = 507; break; } case':':{ words[j] = ch; words[j+1] = '\0'; flag = 508; break; } case'"':{ words[j] = ch; words[j+1] = '\0'; flag = 509; break; } case'%':{ if (ch == '%') words[j++] = ch; words[j] = '\0'; ch = program[i++]; if (ch == '=') { words[j++] = ch; words[j] = '\0'; flag = 510; } else { i--; flag = 511; } break; } case',':{ words[j] = ch; words[j+1] = '\0'; flag = 512; break; } case'#':{ words[j] = ch; words[j+1] = '\0'; flag = 513; break; } case'@':{ words[j] = '#'; flag = 0; break; } default:{ flag = -1; break; } } return flag; } main() { i=0; printf("please input a program end with @"); do { ch = getchar(); program[i++] = ch; }while(ch != '@'); i = 0; do{ flag = Scan(program); if (flag == 200) { printf("(%2d,%4d)",flag,number); } else if (flag == -1) { printf("(%d,error)",flag); } else { printf("(%2d,%4s)",flag,words); } }while (flag != 0); system("pause"); }