fixed #133

ch09/README.md

@@ -163,13 +163,30 @@ while (iter != mid)
         iv.insert(iter, 2 * some_val);
 ```
 
-It's a endless loop. `iter` never equal `mid`.
+**Problems:**
 
-FIXED: (changed the `while` loop)
-```
-while (iter++ != mid)
+1. It's a endless loop. `iter` never equal `mid`.
+2. mid will be invalid after the `insert`.(see [issue 133](https://github.com/Mooophy/Cpp-Primer/issues/133))
+
+**FIXED**:
+
+```cpp
+// cause the reallocation will lead the iterators and references
+// after the insertion point to invalid. Thus, we need to call reserver at first.
+
+vector<int> iv = {0,1,2,3,4,5,6,7,8,9}; // For example.
+iv.reserver(25); // make sure that enough
+
+vector<int>::iterator iter = iv.begin(), mid = iv.begin() + iv.size()/2;
+while (iter != mid)
+    if (*mid == some_val)
+        mid = iv.insert(mid, 2 * some_val);
+    else
+        --mid;
 ```
 
+The complete test codes, check [this](ex9_22.cpp).
+
 ## Exercise 9.23:
 >In the first program in this section on page 346, what would
 the values of val, val2, val3, and val4 be if c.size() is 1?

ch09/ex9_22.cpp

@@ -0,0 +1,30 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+void insertDoubleValue(vector<int> &iv, int some_val)
+{
+    vector<int>::iterator iter = iv.begin(), mid = iv.begin() + iv.size()/2;
+    while (iter != mid)
+        if (*mid == some_val)
+            mid = iv.insert(mid, 2 * some_val);
+        else --mid;
+}
+
+void print(const vector<int> &iv)
+{
+    for (auto i : iv)
+        cout << i << " ";
+    cout << endl;
+}
+
+int main()
+{
+    vector<int> iv = {0,1,2,3,4,5,6,7,8,9};
+    iv.reserve(25);
+    cout << iv.capacity() << endl;
+    insertDoubleValue(iv, 4);
+    print(iv);
+}
+