Solve Exercise 5-19: Omit extra parens in `undcl`

1 files changed, 113 insertions, 0 deletions

diff --git a/ch5/5-19_undcl-no-redundant-parens.c b/ch5/5-19_undcl-no-redundant-parens.c
new file mode 100644
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--- /dev/null
+++ b/ch5/5-19_undcl-no-redundant-parens.c
@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-19: Modify `undcl` so that it does not add redundant parentheses
+ * to declarations.
+ *
+ * Notes: The only circumstance that `undcl` will add extra parens is when it
+ * comes across a pointer. So we look ahead and count pointers, then add them
+ * all at once before output. It's a fairly simple fix.
+ */
+
+#define MAXTOKEN 100
+#define BUFSIZE 100
+#define MAXPTR 10
+
+enum { NAME, PARENS, BRACKETS, TYPE };
+
+int gettoken(void);
+int getch(void);
+void ungetch(int);
+
+char buf[BUFSIZE];
+int bufp = 0;
+int tokentype;
+char token[MAXTOKEN];
+char name[MAXTOKEN];
+char datatype[MAXTOKEN];
+char out[1000];
+
+int gettoken(void) {
+	int c;
+	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;
+	}
+}
+
+int getch(void) {
+	return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) {
+	if (bufp >= BUFSIZE) {
+		printf("ungetch: Too many characters.\n");
+	} else {
+		buf[bufp++] = c;
+	}
+}
+
+int main(void) {
+	int type, pcount, i, c;
+	char temp[MAXTOKEN];
+	char p[MAXPTR];
+	while (gettoken() != EOF) {
+		strcpy(out, token);
+		while ((type = gettoken()) != '\n') {
+			if (type == PARENS || type == BRACKETS) {
+				strcat(out, token);
+			} else if (type == '*') {
+				pcount++;
+				while ((c = getch()) == '*' || c == ' ') {
+					if (c == '*') {
+						if (pcount < (MAXPTR - 1)) {
+							pcount++;
+						} else {
+							break;
+						}
+					}
+				}
+				ungetch(c);
+				for (i = 0; i < pcount; i++) {
+					p[i] = '*';
+				}
+				pcount = 0;
+				p[i] = '\0';
+				sprintf(temp, "(%s%s)", p, 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;
+}