C declaration intepreter from Expert C Programming

c-declaration-interpreter.c

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#define MAXTOKENS 100
#define MAXTOKENLEN 64

enum type_tag { IDENTIFIER, QUALIFIER, TYPE };

struct token 
{
    char type;
    char string[MAXTOKENLEN];
};

int top = -1;
struct token stack[MAXTOKENS];
struct token this;

#define pop stack[top--]
#define push(s) stack[++top] = s

enum type_tag classify_string(void)
{
    char *s = this.string;
    if(!strcmp(s, "const"))
    {
        strcpy(s, "read-only");
        return QUALIFIER;
    }
    if(!strcmp(s, "volatile")) return QUALIFIER;
    if(!strcmp(s, "void")) return TYPE;
    if(!strcmp(s, "char")) return TYPE;
    if(!strcmp(s, "signed")) return TYPE;
    if(!strcmp(s, "unsigned")) return TYPE;
    if(!strcmp(s, "short")) return TYPE;
    if(!strcmp(s, "int")) return TYPE;
    if(!strcmp(s, "long")) return TYPE;
    if(!strcmp(s, "float")) return TYPE;
    if(!strcmp(s, "double")) return TYPE;
    if(!strcmp(s, "struct")) return TYPE;
    if(!strcmp(s, "union")) return TYPE;
    if(!strcmp(s, "enum")) return TYPE;
    return IDENTIFIER;
}

void gettoken(void)
{
    char *p = this.string;

    while((*p = getchar()) == ' ');

    if(isalnum(*p))
    {
        while(isalnum(*++p = getchar()));
        ungetc(*p, stdin);
        *p = '\0';
        this.type = classify_string();
        return;
    }

    if(*p == '*')
    {
        strcpy(this.string, "pointer to");
        this.type = '*';
        return;
    }

    this.string[1] = '\0';
    this.type = *p;
    return;
}

void read_to_first_identifer(void)
{
    gettoken();
    while(this.type != IDENTIFIER)
    {
        push(this);
        gettoken();
    }
    printf("%s is ", this.string);
    gettoken();
}

void deal_with_arrays(void)
{
    while(this.type == '[')
    {
        printf("array ");
        gettoken();
        if(isdigit(this.string[0]))
        {
            printf("0..%d ", atoi(this.string) -1);
            gettoken();
        }
        gettoken();
        printf("of ");
    }
}

void deal_with_function_args(void)
{
    while(this.type != ')')
    {
        gettoken();
    }
    gettoken();
    printf("function returning ");
}

void deal_with_pointers(void)
{
    while(stack[top].type == '*')
    {
        printf("%s ", pop.string);
    }
}

void deal_with_declarator(void)
{
    switch(this.type)
    {
        case '[': deal_with_arrays(); break;
        case '(': deal_with_function_args(); break;
    }

    deal_with_pointers();

    while(top >= 0)
    {
        if(stack[top].type == '(')
        {
            pop;
            gettoken();
            deal_with_declarator();
        }
        else
        {
            printf("%s ", pop.string);
        }
    }
}

int main(int argc, char const *argv[])
{
    read_to_first_identifer();
    deal_with_declarator();
    printf("\n");
    return 0;
}