main.cpp

pl0语言编译器及从中分离的语法分析程序

#include<iostream.h>
#include<fstream.h>
#include<string.h>
#include<stdlib.h>
#include <ctype.h>
#include "pl0.h"

//------------------getch()---get char----------------------------------------
void getch(void){
	if (cc == ll)      //when first char
	{
		if (feof(infile))
		{
			printf("\nPROGRAM INCOMPLETE\n");
			exit(1);
		}//end(if NULL)
		ll = cc = 0;
		while ( (!feof(infile))   //not NULL infile 
			    && ((ch = getc(infile)) != '\n'))
		{
			printf("%c", ch);    //output the char to output one line. 
			line[++ll] = ch;     //store in line[80] to store one line.
		} // while
		printf("\n");            //go to next line after outputting one line.
		line[++ll] = ' ';	
	}//end(if cc==ll)
	ch = line[++cc];             //get the next char
} 
//------getsym()---gets a symbol from input stream.----------------------------
void getsym(void)
{
	int i, k;
	char a[MAXIDLEN + 1];

	while (ch == ' '|| ch == '\t'){   //ignore all space or tab	
		getch();
	}
	if (isalpha(ch))
	{ // symbol is a reserved word or an identifier.
		k = 0;
		do{
			if (k < MAXIDLEN){
				cout<<ch;     //output the reserved word or identifier
			}
			a[k++] = ch;
			getch();	
		}while (isalpha(ch) || isdigit(ch));
		a[k] = 0;
		strcpy(id, a);
		word[0] = id;
		i = NRW;
		while (strcmp(id, word[i--]));
		if (++i){     // symbol is a reserved word
		    cout<<" ->reserved word"<<endl;
		}else{       // symbol is an identifier
			cout<<" ->identifier"<<endl; }
	}
	else if (isdigit(ch))
	{ // symbol is a number.
		do{
			cout<<ch;
			getch();
		}while (isdigit(ch));
		cout<<" ->number"<<endl;
	}
	else if (ch == ':')
	{
		cout<<ch;
		getch();
		if (ch == '='){
			cout<<ch;    // :=
			cout<<" ->avaluate symbol"<<endl;
			getch();
		}
	}
	else if (ch == '>')
	{   cout<<ch;     // >
		getch();
		if (ch == '=')
		{   cout<<ch;   // >=
			getch();
		}
		cout<<" ->symbol"<<endl;
	}
	else if (ch == '<'){   
		cout<<ch;        // <
		getch();
		if (ch == '=')
		{   cout<<ch;    // <=
			getch();
		}
		else if (ch == '>')
		{   cout<<ch;    // <>
			getch();
		}
		cout<<" ->symbol"<<endl;
	}else{ // other tokens--symbols--'+','-','{','}',...
		i = NSYM;
		csym[0] = ch;
		cout<<ch;
		while (csym[i--] != ch);
		if (++i){   
			cout<<" ->symbol"<<endl;
			getch();
		}else{
			exit(1);
		}
	}
} // getsym
////////////////////////////////////////////////
int main(){

	char s[80];
	printf("Please input source file name: "); // get file name to be compiled
	scanf("%s", s);
	if ((infile = fopen(s, "r")) == NULL)
	{
		printf("File %s can't be opened.\n", s);
		exit(1);
	}

	cc = cx = ll = 0; // initialize global variables
	ch = ' ';
    for(int m=0;m<MAXIDLEN;m++){ 
		cout<<endl;
        getsym();
	    while(cc<ll) getsym();
	}//(for m)
	fclose(infile);
	return 0;
}