Chapter 5

1 files changed, 97 insertions, 0 deletions

diff --git a/ex5-1.c b/ex5-1.c
new file mode 100644
index 0000000..9a43c00
--- /dev/null
+++ b/ex5-1.c
@@ -0,0 +1,97 @@
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define PUSHBACK_MAX 10
+typedef struct {
+    FILE* stream;
+    int pushback[PUSHBACK_MAX];
+    int pushback_ix;
+} StreamWithPushback;
+
+StreamWithPushback swpb_new(FILE* f) {
+    StreamWithPushback ret;
+    ret.stream = f;
+    ret.pushback_ix = 0;
+    for (int i=0; i<PUSHBACK_MAX; i++) {
+        ret.pushback[i] = -1;
+    }
+    return ret;
+}
+
+int getch(StreamWithPushback* swpb) {
+    if (swpb->pushback_ix > 0) {
+        int ch = swpb->pushback[swpb->pushback_ix];
+        swpb->pushback_ix--;
+        return ch;
+    }
+    return getc(swpb->stream);
+}
+
+void ungetch(StreamWithPushback* swpb, int ch) {
+    if (swpb->pushback_ix >= PUSHBACK_MAX) {
+        fprintf(stderr, "pushback buffer was full!\n");
+        exit(1);
+    }
+    swpb->pushback[swpb->pushback_ix] = ch;
+    swpb->pushback_ix++;
+}
+
+/* getint:  get next integer from input into *pn */
+int getint(StreamWithPushback* swpb, int *pn) {
+    int c, sign;
+
+    while (isspace(c = getch(swpb))) {}
+
+    if (!isdigit(c) && c != EOF && c != '+' && c != '-') {
+        ungetch(swpb, c);
+        return 0;
+    }
+
+    sign = (c == '-') ? -1 : 1;
+    if (c == '+' || c == '-') {
+        c = getch(swpb);
+        // If c isn't then a digit, then we don't have a number.
+        if (!isdigit(c)) {
+            ungetch(swpb, c);
+            // Push the sign character back as well, don't consume it
+            ungetch(swpb, sign == -1 ? '-' : '+');
+            return 0;
+        }
+    }
+
+    for (*pn = 0; isdigit(c); c = getch(swpb)) {
+        *pn = 10 * *pn + (c - '0');
+    }
+    *pn *= sign;
+
+    if (c != EOF) {
+        ungetch(swpb, c);
+    }
+    return c;
+}
+
+#ifndef test
+
+int main(void) {
+    int p, x;
+    StreamWithPushback swpb = swpb_new(stdin);
+    while ((x = getint(&swpb, &p)) != EOF) {
+        if (x > 0) {
+            printf("%d\n", p);
+        } else {
+            printf("not a number!\n");
+        }
+    } 
+}
+
+#else
+
+#include "CuTest.h"
+
+// I could write unit tests here, using fmemopen
+// instead of reading something off the filesystem.
+
+// But I can't be bothered.
+
+#endif
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