/***********************************************************
* You can use all the programs on  www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact [email protected]
* To find more C programs, do visit www.c-program-example.com
* and browse!
* 
*                      Happy Coding
***********************************************************/

#include<stdio.h>
#include<ctype.h>
#include<string.h>

#define MAXWORD 100

struct nlist{
 struct nlist *next;
 char *name;
 char *defn;
};
void error(int, char*);
int getch(void);
void getdef(void);
int getword(char *,int);
struct nlist *install(char *,char *);
struct nlist *lookup(char *);
void skipblanks(void);
void undef(char *);
void ungetch(int);
void ungets(char *);


//simple version of #define processor
main()
{
 char w[MAXWORD];
 struct nlist *p;
 while(getword(w, MAXWORD) != EOF)
  if(strcmp(w, "#") == 0)
   getdef();
  else if(!isalpha(w[0]))
   printf("%s",w);
  else if ((p == lookup(w)) == NULL)
   printf("%s",w);
  else
   ungets(p->defn);
}

//getdef:get defination and install it
void getdef()
{
 int c,i;
 char def[MAXWORD], dir[MAXWORD], name[MAXWORD];
 skipblanks();
 if(!isalpha(getword(dir,MAXWORD)))
  error(dir[0],"getdef:expecting a directve after #");
 else if(strcmp(dir,"define") == 0) {
  skipblanks();
  if(!isalpha(getword(name, MAXWORD)))
   error(name[0],"getdef:non alpha name expected"):
   else{
    skipblanks();
    for(i = 0;i <  MAXWORD-1; i++)
     if((def[i] = getch()) == EOF || def[i] == 'n')
      break;
    def[i] = '';
    if(i <= 0)
     error('n',"getdef:non alpha in define");
    else
     install(name, def);
   }
 }else if(strcmp(dir,"undef") == 0) {
  skipblanks();
  if(!isalpha(getword(name, MAXWORD)))
   error(name[0],"getdef:non alphain undef"):
   else
    undef(name);
 }else
  error(dir[0],"getdef:expecting a directive after #");
}

//undef:remove a name and defination from the table
int undef(char * name) {
 struct nlist * np1, * np2;

 if ((np1 = lookup(name)) == NULL)  /*  name not found  */
  return 1;

 for ( np1 = np2 = hashtab[hash(name)]; np1 != NULL;
   np2 = np1, np1 = np1->next ) {
  if ( strcmp(name, np1->name) == 0 ) {  /*  name found  */

   /*  Remove node from list  */

   if ( np1 == np2 )
    hashtab[hash(name)] = np1->next;
   else
    np2->next = np1->next;

   /*  Free memory  */

   free(np1->name);
   free(np1->defn);
   free(np1);

   return 0;
  }
 }

 return 1;  /*  name not found  */
}

//error:print error message and skip the rest of the line
void error(int c, char *s)
{
 printf("error:%sn",s);
 while(c != EOF && c != 'n')
  c = getch();
}

//skipblanks:skip blan and tab characters
void skipblanks()
{
 int c;
 while((c = getch()) == ' ' ||c == 't')
  ;
 ungetch(c);
}

/*ungets: push string back onto the input*/
void ungets(char s[])
{
 int len=strlen(s);
 void ungetch(int);
 while (len >0)
  ungetch(s[--len]);
}
/*note: modify the getword function to return 
spaces so that the output resembles the input data.*/

Read more c programs

C Basic
C Strings
K and R C Programs Exercise

You can easily select the code by double clicking on the code area above.

To get regular updates on new C programs, you can Follow @c_program

You can discuss these programs on our Facebook Page. Start a discussion right now,

our page!

Share this program with your Facebook friends now! by liking it

(you can send this program to your friend using this button)

Like to get updates right inside your feed reader? Grab our feed!