Example solution for C++ 101 Exercise 2 (callbacks, and bind)

base/cpp101/fibonacci.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdio.h>
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/callback.h"
+#include "base/strings/string_number_conversions.h"
+
+namespace {
+
+struct FibonacciState {
+  FibonacciState() : i(0), j(1) {}
+
+  int i, j;
+};
+
+int ComputeNextFibonacciNumber(FibonacciState* state) {
+  int next = state->i + state->j;
+  state->i = state->j;
+  state->j = next;
+  return state->i;
+}
+
+base::Callback<int()> MakeFibonacciClosure() {
+  scoped_ptr<FibonacciState> state(new FibonacciState);
+  return base::Bind(&ComputeNextFibonacciNumber, base::Owned(state.release()));
+}
+
+}  // namespace
+
+int main(int argc, char* argv[]) {
+  if (argc <= 1) {
+    printf("%s: missing operand\n", argv[0]);
+    return -1;
+  }
+
+  int n = 0;
+  if (!base::StringToInt(argv[1], &n) || n < 0) {
+    printf("%s: invalid n `%s'\n", argv[0], argv[1]);
+    return -1;
+  }
+
+  base::Callback<int()> fibonacci_closure1 = MakeFibonacciClosure();
+  base::Callback<int()> fibonacci_closure2 = MakeFibonacciClosure();
+  for (int i = 0; i < n; ++i) {
+    int j = fibonacci_closure1.Run();
+    int k = fibonacci_closure2.Run();
+    DCHECK_EQ(j, k);
+    printf("F_%d = %d\n", i, j);
+  }
+
+  return 0;
+}