lexer.c

来自「a compiler in java that parses and creat」· C语言 代码 · 共 53 行

#include "global.h"

char lexbuf[BSIZE];
int lineno = 1;
int tokenval = NONE;

/* lexical analyzer */
int lexan(){
	int t;
	while(1) {
		t=getchar();

		/* strip out white space */
		if( t== ' ' || t== '\t' )
			;
		else if( t== '\n' )
			lineno = lineno + 1;

		/* t is a digit */
		else if( isdigit(t) ) {
			ungetc( t, stdin );
			scanf( "%d", &tokenval );
			return NUM;
		}
		/* t is a letter */
		else if( isalpha(t) ) {
			int p, b = 0;
			while( isalnum(t) ) {
				lexbuf[b] = t;
				t = getchar();
				b = b + 1;
				if( b>=BSIZE )
					error( "Compiler Error ");
			}
			lexbuf[b] = EOS;
			if( t!= EOF)
				ungetc( t, stdin );
			p = lookup(lexbuf);
			if( p == 0)
				p = insert( lexbuf, ID );
			tokenval = p;
			return symtable[p].token;
		}
		else if ( t== EOF )
			return DONE;
		else {
			tokenval = NONE;
			return t;
		}
	}	
}