Exerc 6_5.

chapter_6.structures/6_5.undef/Makefile

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+BINARY=undef
+
+include ../../Exercise_incl.mk

chapter_6.structures/6_5.undef/getline.c

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+# include <stdio.h>
+
+int getline (char *line, int lim)
+{
+  int c;
+  char *l0 = line;
+
+  while (--lim > 0 && (c = getchar()) != EOF && c != '\n')
+    *line++ = c;
+  *line = '\0';
+
+  return c == EOF ? -1 : line - l0;
+}

chapter_6.structures/6_5.undef/getline.h

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+# ifndef GETLINE_H
+# define GETLINE_H
+
+int getline (char *line, int lim);
+
+# endif

chapter_6.structures/6_5.undef/hashtab.c

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+# include <stdio.h>
+# include <stdlib.h>
+# include <string.h>
+
+struct nlist {   /* table entry: */
+  struct nlist *next; /* next entry in chain */
+  char *name;         /* defined name */
+  char *defn;         /* replacement text */
+};
+
+#define HASHSIZE 101
+
+static struct nlist *hashtab[HASHSIZE]; /* pointer table */
+
+/* hash: form hash value for string s */
+unsigned hash (char *s)
+{
+  unsigned hashval;
+
+  for (hashval = 0; *s != '\0'; s++)
+    hashval = *s + 31 * hashval;
+  return hashval % HASHSIZE;
+}
+
+/* lookup: look for s in hashtab */
+struct nlist *lookup (char *s)
+{
+  struct nlist *np;
+
+  for (np = hashtab[hash(s)]; np != NULL; np = np->next)
+    if (strcmp(s, np->name) == 0)
+      return np;  /* found */
+  return NULL;    /* not found */
+}
+
+/* make a duplicate of s */
+char *strdup (char *s)
+{
+  char *p;
+
+  p = (char *) malloc(strlen(s)+1); /* +1 for '\0' */
+  if (p != NULL)
+    strcpy(p, s);
+  return p;
+}
+
+/* install: put (name, defn) in hashtab */
+struct nlist *install (char *name, char *defn)
+{
+  struct nlist *np;
+  unsigned hashval;
+
+  if ((np = lookup(name)) == NULL) { /* not found */
+    np = (struct nlist *) malloc(sizeof(*np));
+    if (np == NULL || (np->name = strdup(name)) == NULL)
+      return NULL;
+    hashval = hash(name);
+    np->next = hashtab[hashval];
+    hashtab[hashval] = np;
+  } else       /* already there */
+    free((void *) np->defn);  /*free previous defn */
+  if ((np->defn = strdup(defn)) == NULL)
+    return NULL;
+  return np;
+}
+
+/* free_node: free the memory taken by nlist, including internal strings */
+void free_node (struct nlist *np)
+{
+  free(np->name);
+  free(np->defn);
+  free(np);
+}
+
+/* undef: remove name from hashtab */
+int undef (char *name)
+{
+  struct nlist *np, *prev;
+
+  if ((np = hashtab[hash(name)]) != NULL) {
+    if (strcmp(np->name, name) == 0) {
+      hashtab[hash(name)] = np->next;
+      free_node(np);
+      return 1;
+    } else {
+      for (prev = np, np = np->next; np != NULL; prev = np, np = np->next)
+        if (strcmp(name, np->name) == 0) {
+          prev->next = np->next;
+          free_node(np);
+          return 1;
+        }
+    }
+  }
+
+  return 0;
+}
+
+/* print_hashtab: print hash table content */
+void print_hashtab (void)
+{
+  int i;
+  struct nlist *np;
+
+  for (i = 0; i < HASHSIZE; i++)
+    for (np = hashtab[i]; np != NULL; np = np->next)
+      printf("[%d] '%s': '%s'\n", i, np->name, np->defn);
+}

chapter_6.structures/6_5.undef/hashtab.h

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+# ifndef HASHTAB_H
+# define HASHTAB_H
+
+/* lookup: look for s in hashtab */
+struct nlist *lookup (char *s);
+/* install: put (name, defn) in hashtab */
+struct nlist *install (char *name, char *defn);
+/* undef: remove name from hashtab */
+int undef (char *name);
+/* print_hashtab: print hash table content */
+void print_hashtab (void);
+
+# endif

chapter_6.structures/6_5.undef/main.c

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+# include <stdio.h>
+# include <string.h>
+# include "getline.h"
+# include "hashtab.h"
+
+# define BUFSIZE 1024
+
+int main ()
+{
+  char line[BUFSIZE], name[BUFSIZE], defn[BUFSIZE];
+
+  while (getline(line, BUFSIZE) != -1)
+    if (line[0] == '+') {
+      int li = 2, ni = 0, di = 0;
+      while (line[li] != ' ' && line[li] != '\0')
+        name[ni++] = line[li++];
+      if (line[li] == '\0') {
+        printf("ERROR! unexpected end of line while reading definition");
+        return 0;
+      }
+      name[ni] = '\0';
+      li++;
+      while (line[li] != '\0')
+        defn[di++] = line[li++];
+      defn[di] = '\0';
+      install(name, defn);
+    }
+    else if (line[0] == '-') {
+      int li = 2, ni = 0;
+      while (line[li] != '\0')
+        name[ni++] = line[li++];
+      name[ni] = '\0';
+      undef(name);
+    } else {
+      printf("unrecognised operation '%c', should be '+' or '-'.\n", line[0]);
+      return 0;
+    }
+
+  print_hashtab();
+
+  return 0;
+}

chapter_6.structures/6_5.undef/tests/0_defs.tin

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++ some other
++ some different
++ some last one
++ any any single time

chapter_6.structures/6_5.undef/tests/0_defs.tout

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+[5] 'some': 'last one'
+[91] 'any': 'any single time'

chapter_6.structures/6_5.undef/tests/1_undefs.tin

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++ once once upon a time
++ this this one is safe
++ delme you should not see this!
++ delete this one should also be deleted
++ fun fun fun fun
+- delme
++ not ton
+- delete
++ end .

chapter_6.structures/6_5.undef/tests/1_undefs.tout

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+[32] 'this': 'this one is safe'
+[52] 'fun': 'fun fun fun'
+[63] 'once': 'once upon a time'
+[76] 'end': '.'
+[86] 'not': 'ton'