名称空间

base/CMakeLists.txt

@@ -45,4 +45,6 @@ add_executable(test10001 namespacetest/test10001.cpp)
 add_executable(auto namespacetest/auto.cpp)
 add_executable(external namespacetest/external.cpp)
 add_executable(support namespacetest/support.cpp)
-add_executable(ststic namespacetest/ststic.cpp)
+add_executable(ststic namespacetest/ststic.cpp)
+add_executable(newplace namespacetest/newplace.cpp)
+add_executable(namessp namespacetest/namessp.cpp)

base/namespacetest/namesp.cpp

@@ -0,0 +1,44 @@
+//
+// Created by zhuyijun on 2021/8/16.
+//
+
+#include <iostream>
+#include "namesp.h"
+
+namespace pers {
+    using std::cout;
+    using std::cin;
+    using std::endl;
+
+    void getPerson(Person &rp) {
+        cout << "Enter first name: ";
+        cin >> rp.fname;
+        cout << "Enter left name: ";
+        cin >> rp.lname;
+    }
+
+    void showPerson(const Person &rp) {
+        cout << rp.lname << ", " << rp.fname << endl;
+    }
+}
+
+namespace debts {
+    void getDebt(Debt &rd) {
+        getPerson(rd.name);
+        std::cout << "Enter debt: ";
+        std::cin >> rd.amount;
+    }
+
+    void showDebt(const Debt &rd) {
+        showPerson(rd.name);
+        std::cout << " : $" << rd.amount << std::endl;
+    }
+
+    double sumDebts(const Debt ar[], int n) {
+        double total = 0;
+        for (int i = 0; i < n; ++i) {
+            total += ar[i].amount;
+        }
+        return total;
+    }
+}

base/namespacetest/namesp.h

@@ -0,0 +1,32 @@
+//
+// Created by zhuyijun on 2021/8/16.
+//
+
+#include <string>
+
+namespace pers {
+    struct Person {
+        std::string fname;
+        std::string lname;
+    };
+
+    void getPerson(Person &);
+
+    void showPerson(const Person &);
+}
+namespace debts {
+    using namespace pers;
+    struct Debt {
+        Person name;
+        double amount;
+    };
+
+    void getDebt(Debt &);
+
+    void showDebt(const Debt &);
+
+    double sumDebts(const Debt ar[], int n);
+}
+
+
+

base/namespacetest/namessp.cpp

@@ -0,0 +1,48 @@
+//
+// Created by zhuyijun on 2021/8/16.
+//
+
+#include <iostream>
+#include "namesp.h"
+
+void other(void);
+void another(void);
+/**
+ * 编译命令
+ * g++ .\namesp.cpp .\namessp.cpp -o test
+ * @return
+ */
+int main() {
+    using debts::Debt;
+    using debts::showDebt;
+    Debt golf = {{"Benny", "Goatsniff"}, 120.0};
+    showDebt(golf);
+    other();
+    another();
+    return 0;
+}
+
+void other(void) {
+    using std::cout;
+    using std::endl;
+    using namespace debts;
+    Person dg = {"Doodles", "Glister"};
+    showPerson(dg);
+    Debt zippy[3];
+    int i;
+    for (i = 0; i < 3; ++i) {
+        getDebt(zippy[i]);
+    }
+    for (i = 0; i < 3; ++i) {
+        showDebt(zippy[i]);
+    }
+    cout << "Total debt: $" << sumDebts(zippy, 3) << endl;
+    return;
+}
+
+void another(void) {
+    using pers::Person;
+    Person collector = {"Milo", "Rightshift"};
+    pers::showPerson(collector);
+    std::cout << std::endl;
+}

base/namespacetest/newplace.cpp

@@ -0,0 +1,60 @@
+//
+// Created by zhuyijun on 2021/8/16.
+//
+
+#include <iostream>
+#include <new>
+
+using namespace std;
+
+const int BUF = 512;
+const int N = 5;
+char buffer[BUF];
+
+int main() {
+
+    double *pd1, *pd2;
+    int i;
+    cout << "Calling new and placement new:\n";
+    pd1 = new double[N];
+    pd2 = new(buffer) double[N];
+    for (int i = 0; i < N; ++i) {
+        pd2[i] = pd1[i] = 1000 + 20.0 * i;
+    }
+    cout << "Memory addresses:\n" << " heap: " << pd1 << " static: " << (void *) buffer << endl;
+    cout << "Memory contents:\n";
+    for (int i = 0; i < N; ++i) {
+        cout << pd1[i] << " at" << &pd1[i] << "; ";
+        cout << pd2[i] << " at" << &pd2[i] << endl;
+    }
+    cout << "\n Calling new and placement new a second time:\n";
+    double *pd3, *pd4;
+    pd3 = new double[N];
+    pd4 = new(buffer) double[N];
+    for (int i = 0; i < N; ++i) {
+        pd4[i] = pd3[i] = 1000 + 40.0 * i;
+    }
+    cout << "Memory contents:\n";
+    for (int i = 0; i < N; ++i) {
+        cout << pd3[i] << " at" << &pd3[i] << "; ";
+        cout << pd4[i] << " at" << &pd4[i] << endl;
+    }
+    cout << "\n Calling new and placement new a second time:\n";
+    delete[]pd1;
+    pd1 = new double[N];
+    pd2 = new(buffer + N * sizeof(double)) double[N];
+    for (int i = 0; i < N; ++i) {
+        pd2[i] = pd1[i] = 1000 + 60.0 * i;
+    }
+    cout << "Memory contents:\n";
+    for (int i = 0; i < N; ++i) {
+        cout << pd1[i] << " at" << &pd1[i] << "; ";
+        cout << pd2[i] << " at" << &pd2[i] << endl;
+    }
+    delete[]pd1;
+    delete[]pd3;
+//    delete[]pd2;
+//    delete[]pd4;
+    return 0;
+}
+