Question

I was making this very simple lex program (just an introductory program). But on compiling lex.yy.c, I am getting this error as:

inToPostfix.l:26: error: ‘struct stackoperand’ has no member named ‘top’
inToPostfix.l:32: error: ‘struct stackoperator’ has no member named ‘top’....

I could not make any reason for this error as I already have defined top in the specified structure.
Can you see any reason for it?

Code is posted at http://pastebin.com/d5f059c1d

Answer 1

Move line 3 to line 16.

You also need to remove the initializers from the structure declarations – at least for C (but the C++ compiler didn’t think much of it either).

struct stackoperator
{
char stack[10];
int top =-1;
};

To:

struct stackoperator
{
char stack[10];
int top;
};

In the actions, you also need to declare ‘ch’.

You also need to declare your functions – I made them static. This compiles (assuming you have a C99 compiler – the designated initializers won’t work with C89 compilers):

%{
#include<stdio.h>

struct stackoperator
{
char stack[10];
int top;
};

struct stackoperand
{
int stack[10][2];
int top;
};
struct stackoperator operator = { .top = -1 };
struct stackoperand operand = { .top = -1 };
int num=0;
static void push(int num,int flag);
static int pop(void);
static int precedence(char a,char b);
%}

%%

[0-9]   {num=num*10+(*yytext-'0');push(num,1);}
[-+*/]  {
        if(precedence(operator.top,*yytext)) {
            char ch=pop();
            push(ch,0);
            operand.stack[operand.top][1]=1;
        }
        push(*yytext,0);
    }
[ \t]    ;
[\n]      {
        char ch;
        while(operator.top!=-1)
        {
            ch=pop();
            push(ch,0);
        }
        int i=0;
        while(i<=operand.top)
        {
            if(operand.stack[operand.top][1]==1)
                printf(" %c ",operand.stack[operand.top][0]);
            else
                printf(" %d ",operand.stack[operand.top][0]);
        }
    }
%%

static void push(int num,int flag)
{
    if(flag)
    {       operand.top++;
        operand.stack[operand.top][0]=num;
        operand.stack[operand.top][1]=0;
    }
    else
        operator.stack[++operator.top]=num;
}

static int pop(void)
{
    return operator.stack[operator.top--];
}

static int precedence(char a,char b)
{
    if(operator.top==-1)
        return 0;

    if((a=='*'||a=='/') && (b=='+'||b=='-'))
        return 1;
    else
        return 0;
}