add memory allocation

03.Advanced/MemoryAllocation.cpp

+#include <iostream>
+using namespace std;
+
+int main() {
+
+    cout << "----- Variable memory allocation -----" << endl;
+    // 基础变量的内存分配
+    // 初始化为 null 的指针
+    double * pvalue  = NULL;
+
+    // 为变量请求内存
+    if(!(pvalue  = new double)) { 
+
+        // 如果自由存储区已被用完，可能无法成功分配内存。
+        cout << "Error: out of memory." <<endl;
+        exit(1);
+
+    }
+
+    // 在分配的地址存储值
+    *pvalue = 29494.99;
+    cout << "Value of pvalue : " << *pvalue << endl;
+
+    // 释放 pvalue 所指向的内存
+    delete pvalue;
+
+    cout << "----- 2D array memory allocation -----" << endl;
+    // 二维数组的内存分配
+    int ROW = 2;
+    int COL = 3;
+    
+    // 为行分配内存
+    double ** p2dArray  = new double * [ROW];
+    double ** currRowPtr;
+    double * currColPtr;
+
+    // 为列分配内存
+    for(int i = 0; i < ROW; i++) {
+
+        p2dArray[i] = new double[COL];
+
+    }
+
+    // 指向起始位置
+    currRowPtr = p2dArray;
+    // 循环行
+    for (int i = 0; i < ROW; i++) {
+
+        cout << "Pointer of row[" << i << "] is: [";
+        cout << *currRowPtr << "] at [" << currRowPtr << "]" << endl;
+
+        // 循环列
+        currColPtr = *currRowPtr;
+        for (int j = 0; j < COL; j++) {
+
+            cout << "Pointer of col[" << j << "] is: [";
+            cout << *currColPtr << "] at [" << currColPtr << "]" << endl;
+
+            currColPtr++;
+
+        }
+
+        currRowPtr++;
+
+    }
+
+    // 释放内存，释放的时候，需要确保指针指向的位置是已经被分配过的
+    // 否则会出异常pointer being freed was not allocate
+    // delete * p2dArray;
+    // delete * currRowPtr;
+    // delete currColPtr;
+
+    cout << "----- Object memory allocation -----" << endl;
+    // 对象的内存分配
+    class Box {
+
+        public:
+
+            Box() {
+
+                cout << "调用构造函数！" <<endl;
+
+            }
+
+            ~Box() {
+
+                cout << "调用析构函数！" <<endl;
+
+            }
+
+    };
+
+    Box * myBoxArray = new Box[4]; //
+    Box * currBox = myBoxArray;
+
+    for (int i = 0; i < 4; i++) {
+
+        cout << "Pointer of myBoxArray[" << i << "] at [" << currBox << "]" << endl;
+        currBox++;
+
+    }
+
+    delete [] myBoxArray;
+
+}
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