Solve Exercise 5-1: fixed getint()

1 files changed, 65 insertions, 0 deletions

diff --git a/ch5/5-01_getint-fixed.c b/ch5/5-01_getint-fixed.c
new file mode 100644
index 0000000..8d53ba6
--- /dev/null
+++ b/ch5/5-01_getint-fixed.c
@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-1: As written, getint treats a + or - not followed by a digit as
+ * a valid representation of zero. Fix it to push such a character back on the
+ * input.
+ */
+
+#define BUFSIZE 100
+
+int getch(void);
+void ungetch(int);
+int getint(int *);
+
+char buf[BUFSIZE];
+int bufp = 0;
+
+int main() {
+	int foo;
+	int *bar = &foo;
+	while (getint(bar) > 0) {
+		printf("%d\n", foo);
+	}
+	return 0;
+}
+
+int getint(int *pn) {
+	int c, sign;
+
+	while (isspace(c = getch())) {
+	}
+	if (!isdigit(c) && c != EOF && c != '+' && c != '-') {
+		ungetch(c);
+		return 0;
+	}
+	sign = (c == '-') ? -1 : 1;
+	if (c == '+' || c == '-') {
+		c = getch();
+	}
+	if (!isdigit(c)) {
+		return 0;
+	}
+	for (*pn = 0; isdigit(c); c = getch()) {
+		*pn = 10 * *pn + (c - '0');
+	}
+	*pn *= sign;
+	if (c != EOF) {
+		ungetch(c);
+	}
+	return 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;
+	}
+}