add

Author: Hawstein

13.1

@@ -0,0 +1,31 @@
+#include <iostream>
+#include <fstream>
+using namespace std;
+
+void printLastKLines(ifstream &fin, int k){
+    string line[k];
+    int lines = 0;
+    string tmp;
+    while(getline(fin, tmp) && !fin.eof()){
+        line[lines%k] = tmp;
+        ++lines;
+    }
+    int start, cnt;
+    if(lines < k){
+        start = 0;
+        cnt = lines;
+    }
+    else{
+        start = lines%k;
+        cnt = k;
+    }
+    for(int i=0; i<cnt; ++i)
+        cout<<line[(start+i)%k]<<endl;
+}
+int main(){
+    ifstream fin("13.1.in");
+    int k = 4;
+    printLastKLines(fin, k);
+    fin.close();
+    return 0;
+}

13.1.cpp

@@ -0,0 +1,7 @@
+one
+two
+three 3
+last 4 lines:begin
+the second line
+continue
+end

13.1.in

@@ -0,0 +1,65 @@
+#include <iostream>
+#include <cstdlib>
+using namespace std;
+
+template <typename T>
+class SmartPointer{
+public:
+    SmartPointer(T* ptr){
+        ref = ptr;
+        ref_count = (unsigned*)malloc(sizeof(unsigned));
+        *ref_count = 1;
+    }
+	
+    SmartPointer(SmartPointer<T> &sptr){
+        ref = sptr.ref;
+        ref_count = sptr.ref_count;
+        ++*ref_count;
+    }
+	
+    SmartPointer<T>& operator=(SmartPointer<T> &sptr){
+        if (this != &sptr) {
+            if (--*ref_count == 0){
+                clear();
+                cout<<"operator= clear"<<endl;
+            }
+            
+            ref = sptr.ref;
+            ref_count = sptr.ref_count;
+            ++*ref_count;
+        }
+        return *this;
+    }
+	
+    ~SmartPointer(){
+        if (--*ref_count == 0){
+            clear();
+            cout<<"destructor clear"<<endl;
+        }
+    }
+	
+    T getValue() { return *ref; }
+    
+private:
+    void clear(){
+        delete ref;
+        free(ref_count);
+        ref = NULL; // 避免它成为迷途指针
+        ref_count = NULL;
+    }
+   
+protected:	
+    T *ref;
+    unsigned *ref_count;
+};
+
+int main(){
+    int *ip1 = new int();
+    *ip1 = 11111;
+    int *ip2 = new int();
+    *ip2 = 22222;
+    SmartPointer<int> sp1(ip1), sp2(ip2);
+    SmartPointer<int> spa = sp1;
+    sp2 = spa;
+    return 0;
+}