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1.词法分析程序的功能:
组织输入、扫描、分析、输出;
接收字符串形式的源程序,按照源程序输入的次序依次扫描源程序,在扫描的同时根据语言的词法规则识别出具有独立意义的单词,并产生与源程序等价的属性字(Token)流 .
(1) 只要不修改接口,则词法分析器所作的修改不会影响整个编译器,且词法分析器易于维护;
(2) 整个编译器结构简捷、清晰;
(3) 可以采用有效的方法和工具进行处理。
2.符号与种别码对照表:
3.源程序及说明
#include<stdio.h> #include<string.h> #include<stdlib.h> char TOken[10];//分开进行比较 char ch; /*char rwtab[6]={"begin","if","then","while","do","end"};*/ char r1[]={"auto"}; char r2[]={"break"}; char r3[]={"case"}; char r4[]={"char"}; char r5[]={"const"}; char r6[]={"continue"}; char r7[]={"default"}; char r8[]={"do"}; char r9[]={"double"}; char r10[]={"else"}; char r11[]={"enum"}; char r12[]={"extern"}; char r13[]={"float"}; char r14[]={"for"}; char r15[]={"goto"}; char r16[]={"if"}; char r17[]={"int"}; char r18[]={"long"}; char r19[]={"register"}; char r20[]={"return"}; char r21[]={"short"}; char r22[]={"signed"}; char r23[]={"sizeof"}; char r24[]={"static"}; char r25[]={"struct"}; char r26[]={"switch"}; char r27[]={"typedef"}; char r28[]={"union"}; char r29[]={"unsigned"}; char r30[]={"void"}; char r31[]={"volatile"}; char r32[]={"while"}; char r33[]={"end"}; char r34[]={"include"}; char r35[]={"stdio"}; char r36[]={"string"}; char r37[]={"main"}; char r38[]={"stdlib"};//这是我定义的 char A[10000];//输入的所有值 int syn,row; int n,m,p,sum,j; static int i = 0; void scaner(); int main() { row = 0 ; p = 0 ; printf("Please input string:(end of ‘@‘)\n"); do { scanf("%c",&ch); A[p]=ch; p++; }//输入值到数组A【】中,以@结束 while(ch!=‘@‘); do { scaner();//进入函数进行判定 switch(syn) { case 40: printf("(%d,%d)\n",syn,sum); break;//如果是40,那么就是数字 case 0: printf("(%d,%c)\n",syn,TOken[0]);break;//如果是0,那么是@ 结束 case -2: row=row++;break; default: printf("(%d,%s)\n",syn,TOken);break;//否则,就是变量名、关键词 } } while (syn!=0); } void scaner() { /* 共分为三大块,分别是标示符、数字、符号,对应下面的 if else if 和 else */ for(n=0;n<7;n++) TOken[n]=0;//每次循环完就清零 ch=A[i]; while(ch==‘ ‘||ch==‘\n‘)//如果字符是空格或者回车,跳过 { i++; ch=A[i]; } if((ch>=‘a‘&&ch<=‘z‘)||(ch>=‘A‘&&ch<=‘Z‘)) //可能是标示符或者变量名 { m=0; while((ch>=‘0‘&&ch<=‘9‘)||(ch>=‘a‘&&ch<=‘z‘)||(ch>=‘A‘&&ch<=‘Z‘))//找到一个变量名或者关键字,直到遇到空格为止 { TOken[m]=ch;m++; i++;ch=A[i]; } TOken[m]=‘\0‘; //将识别出来的字符和已定义的标示符作比较, //因为定义的begin为1,if为2...... if(strcmp(TOken,r1)==0){syn=1;} else if(strcmp(TOken,r2)==0){syn=2; } else if(strcmp(TOken,r3)==0){syn=3;} else if(strcmp(TOken,r4)==0){syn=4;} else if(strcmp(TOken,r5)==0){syn=5;} else if(strcmp(TOken,r6)==0){syn=6;} else if(strcmp(TOken,r7)==0){syn=7;} else if(strcmp(r8,TOken)==0){syn=8;} else if(strcmp(r9,TOken)==0){syn=9;} else if(strcmp(r10,TOken)==0){syn=10;} else if(strcmp(r11,TOken)==0){syn=11;} else if(strcmp(r12,TOken)==0){syn=12;} else if(strcmp(r13,TOken)==0){syn=13;} else if(strcmp(r14,TOken)==0){syn=14;} else if(strcmp(r15,TOken)==0){syn=15;} else if(strcmp(r16,TOken)==0){syn=16;} else if(strcmp(r17,TOken)==0){syn=17;} else if(strcmp(r18,TOken)==0){syn=18;} else if(strcmp(r19,TOken)==0){syn=19;} else if(strcmp(r20,TOken)==0){syn=20;} else if(strcmp(r21,TOken)==0){syn=21;} else if(strcmp(r22,TOken)==0){syn=22;} else if(strcmp(r23,TOken)==0){syn=23;} else if(strcmp(r24,TOken)==0){syn=24;} else if(strcmp(r25,TOken)==0){syn=25;} else if(strcmp(r26,TOken)==0){syn=26;} else if(strcmp(r27,TOken)==0){syn=27;} else if(strcmp(r28,TOken)==0){syn=28;} else if(strcmp(r29,TOken)==0){syn=29;} else if(strcmp(r30,TOken)==0){syn=30;} else if(strcmp(r31,TOken)==0){syn=31;} else if(strcmp(r32,TOken)==0){syn=32;} else if(strcmp(r33,TOken)==0){syn=33;} else if(strcmp(r34,TOken)==0){syn=34;} else if(strcmp(r35,TOken)==0){syn=35;} else if(strcmp(r36,TOken)==0){syn=36;} else if(strcmp(r37,TOken)==0){syn=37;} else if(strcmp(r38,TOken)==0){syn=38;} else{syn=100;} //变量名 } else if((ch>=‘0‘&&ch<=‘9‘)) //数字 { sum=0; while((ch>=‘0‘&&ch<=‘9‘)) { sum=sum*10+ch-‘0‘;//显示其数字sum i++; ch=A[i]; } syn=40; } else switch(ch) //其他字符 { case‘<‘:m=0;TOken[m]=ch;m++; i++;ch=A[i]; if(ch==‘=‘)//<>为22 { syn=41; TOken[m]=ch;m++;i++; } else { syn=46; } break; case‘>‘:m=0;TOken[m]=ch;m++; i++;ch=A[i]; if(ch==‘=‘) { syn=42; TOken[m]=ch;m++;i++; } else { syn=47; } break; case‘:‘:m=0;TOken[m]=ch;m++; i++;ch=A[i]; if(ch==‘=‘) { syn=44; TOken[m]=ch;m++;i++; } else { syn=49; } break; case‘@‘:syn=0;TOken[0]=ch;i++;break; case‘=‘:syn=48;TOken[0]=ch;i++;break; case‘#‘:syn=50;TOken[0]=ch;i++;break; case‘+‘:syn=50;TOken[0]=ch;i++;break; case‘-‘:syn=51;TOken[0]=ch;i++;break; case‘*‘:syn=52;TOken[0]=ch;i++;break; case‘/‘:syn=53;TOken[0]=ch;i++;break; case‘(‘:syn=54;TOken[0]=ch;i++;break; case‘)‘:syn=55;TOken[0]=ch;i++;break; case‘{‘:syn=56;TOken[0]=ch;i++;break; case‘}‘:syn=57;TOken[0]=ch;i++;break; case‘;‘:syn=58;TOken[0]=ch;i++;break; case‘.‘:syn=59;TOken[0]=ch;i++;break; case‘\‘‘:syn=60;TOken[0]=ch;i++;break; case‘\n‘:syn=-2;break; default: syn=-1;break; } }
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原文地址:http://www.cnblogs.com/bjdx1314/p/5924495.html