text1.cpp

语法分析器 可用 没什么可以补充了。自己看吧

// the scanner implementation for the TINY compiler
#include "globals.h"
#include "util.h"
#include "scan.h"

//states in scanner DFA
typedef enum
{
START,INASSIGN,INCOMMENT,INNUM,INID,DONE
}StateType;

//lexeme of identifier or reserved word
char tokenString[MAXTOKENLEN+1];

//BUFLEN = lenght of the input buffer for source code lines
#define BUFLEN 256

static char lineBuf[BUFLEN];//holds the current lines
static int linepos = 0; //current position in linebuf
static int bufsize = 0;//current size of buffer string

//getNextChar fetches the next non-blank character from lineBuf
//reading in a new line if lineBuf is exhausted
static char getNextChar(void)
{
if(!(linepos<bufsize))
{
lineno++;
if (fgets(lineBuf,BUFLEN-1,source))
{
if(EchoSource)
fprintf(listing,"%d:%s",lineno,lineBuf);
bufsize = strlen(lineBuf);
linepos = 0;
return lineBuf[linepos++];
}
else return EOF;
}
else return lineBuf[linepos++];
}

//ungetNextChar backtracks one character in linebuf
static void ungetNextChar(void)
{
linepos--;
}

//lookup table of reserved words
static struct
{
char* str;
TokenType tok;
}reservedWords[MAXRESERVED]
={{"if",IF},{"then",THEN},{"else",ELSE},{"end",END},
{"repeat",REPEAT},{"until",UNTIL},{"read",READ},{"write",WRITE}};

//lookup an identifier to see if it is a reserved word
//uses linear search
static TokenType reservedLookup(char* s)
{
int i;
for(i=0;i<MAXRESERVED;i++)
if(!strcmp(s,reservedWords[i].str))
return reservedWords[i].tok;
return ID;
}

// the primary function of the scanner

//function getToken returns the next token in source file
TokenType getToken(void)
{
//index for storing into tokenString
int tokenStringIndex = 0;
//holds current token to be returned
TokenType currentToken;
//current state - always begins at START
StateType state = START;
//flag to indicate save to tokenString
int save;
while (state!=DONE)
{
char c = getNextChar();
save = TRUE;
switch(state)
{
case START:
if(isdigit(c))
state = INNUM;
else if(isalpha(c))
state = INID;
else if(c==':')
state = INASSIGN;
else if((c==' ')||(c=='\t')||(c=='\n'))
save = FALSE;
else if(c=='{')
{
save = FALSE;
state = INCOMMENT;
}
else{
state = DONE;
switch(c)
{
case EOF:
save = FALSE;
currentToken = ENDFILE;
break;
case '=':
currentToken = EQ;
break;
case '<':
currentToken = LT;
break;
case '+':
currentToken = PLUS;
break;
case '-':
currentToken = MINUS;
break;
case '*':
currentToken = TIMES;
break;
case '/':
currentToken = OVER;
break;
case '(':
currentToken = LPAREN;
break;
case ')':
currentToken = RPAREN;
break;
case ';':
currentToken = SEMI;
break;
default:
currentToken = ERROR;
break;
}
}
break;
case INCOMMENT:
save = FALSE;
if(c=='}')state = START;
break;
case INASSIGN:
state = DONE;
if(c=='=')
currentToken = ASSIGN;
else{
//backup in the input
ungetNextChar();
save = FALSE;
currentToken = ERROR;
}
break;
case INNUM:
if(!isdigit(c))
{
//backup in the input
ungetNextChar();
save = FALSE;
state = DONE;
currentToken = NUM;
}
break;
case INID:
if(!isalpha(c))
{
//backup in the input
ungetNextChar();
save = FALSE;
state = DONE;
currentToken = ID;
}
break;
case DONE:
default://should never happen
fprintf(listing, "Scanner Bug: state = %d\n",state);
state = DONE;
currentToken = ERROR;
break;
}
if((save)&&(tokenStringIndex <= MAXTOKENLEN))
tokenString[tokenStringIndex++] = c;
if (state == DONE)
{
tokenString[tokenStringIndex] = '\0';
if(currentToken == ID)
currentToken = reservedLookup(tokenString);
}
}
if(TraceScan){
fprintf(listing,"\t%d:",lineno);
printToken(currentToken,tokenString);
}
return currentToken;
}//end getToken