added undcl

Author: satyajitghana

Chapter-5/undcl/buffer.c

@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <string.h>
+#define BUFSIZE 100
+
+int buf[BUFSIZE]; /* buffer for ungetch */
+int bufp = 0; /* buffer pointer (not a real pointer) */
+
+int getch(void) /* get a (possibly pushed back) character */ {
+    return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) /* push character back on input */ {
+    if (bufp >= BUFSIZE)
+        printf("ungetch : too many characters\n");
+    else
+        buf[bufp++] = c;
+}
+
+void ungets(char s[]) /* push string s back to input */ {
+    int i = strlen(s);
+    while (i > 0) ungetch(s[--i]);
+}

Chapter-5/undcl/buffer.h

@@ -0,0 +1,10 @@
+#ifndef BUFFER_H
+#define BUFFER_H
+
+int getch(void);
+
+void ungetch(int);
+
+void ungets(char []);
+
+#endif

Chapter-5/undcl/main.c

@@ -0,0 +1,103 @@
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#define MAXTOKEN 100
+
+enum { NAME, PARENS, BRACKETS };
+
+void dcl(void);
+void dirdcl(void);
+
+int gettoken(void);         
+int tokentype;              /* type of last token */
+char token[MAXTOKEN];       /* last token string */
+char name[MAXTOKEN];        /* indetifier name */
+char datatype[MAXTOKEN];    /* data type = char, int, etc. */
+char out[1024];             /* output string */
+
+/* undcl: convert word description to declaration */
+int main() {
+    int type;
+    char temp[MAXTOKEN];
+
+    while (gettoken() != EOF) {     /* 1st token on line */
+        strcpy(out, token);    /* is the datatype */
+        while ((type = gettoken()) != '\n')
+            if (type == PARENS || type == BRACKETS)
+                strcat(out, token);
+            else if (type == '*') {
+                sprintf(temp, "(*%s)", out);
+                strcpy(out, temp);
+            } else if (type == NAME) {
+                sprintf(temp, "%s %s", token, out);
+                strcpy(out, temp);
+            } else
+                printf("invalid input at %s\n", token);
+        printf("%s\n", out);
+    }
+    return 0;
+}
+
+/* dcl: parse a declarator */
+void dcl(void) {
+    int ns;
+
+    for (ns = 0; gettoken() == '*'; ) /* count *'s */
+        ns++;
+    dirdcl();
+    while (ns-- > 0)
+        strcat(out, " pointer to");
+}
+
+/* dirdcl: parse a direct declarator */
+void dirdcl(void) {
+    int type;
+
+    if (tokentype == '(') {         /* ( dcl ) */
+        dcl();
+        if (tokentype != ')')
+            printf("error: missing )\n");
+    } else if (tokentype == NAME)   /* variable name */
+        strcpy(name, token);
+    else
+        printf("error: expected name or (dcl)\n");
+    while ((type = gettoken()) == PARENS || type  == BRACKETS)
+        if (type == PARENS)
+            strcat(out, " function returning");
+        else {
+            strcat(out, " array");
+            strcat(out, token);
+            strcat(out, " of");
+        }
+}
+
+int gettoken(void) /* return next token */ {
+    int c, getch(void);
+    void ungetch(int);
+    char *p = token;
+
+    while((c = getch()) == ' ' || c == '\t')
+        ;
+    if (c == '(') {
+        if ((c = getch()) == ')') {
+            strcpy(token, "()");
+            return tokentype = PARENS;
+        } else {
+            ungetch(c);
+            return tokentype = '(';
+        }
+    } else if (c == '[') {
+        for (*p++ = c; (*p++ = getch()) != ']'; )
+            ;
+        *p = '\0';
+        return tokentype = BRACKETS;
+    } else if (isalpha(c)) {
+        for (*p++ = c; isalnum(c = getch()); )
+            *p++ = c;
+        *p = '\0';
+        ungetch(c);
+        return tokentype = NAME;
+    } else
+        return tokentype = c;
+}