回答編集履歴
1
追記
test
CHANGED
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@@ -29,3 +29,153 @@
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myclass b = a;
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としたとき、a.p と b.p は別領域となります(からa,bが廃棄されるとき二重解放になりません)
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[追記] 領域のnew/delete の様子をプリントしてみました:
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```C++
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#include <iostream>
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#include <cstdlib>
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using namespace std;
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class myclass {
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int* p;
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public:
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myclass(int i);
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myclass(const myclass& ob);
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~myclass() { std::cout << "delete " << (void*)p << "\n"; delete p; }
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friend int getval(myclass o);
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};
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myclass::myclass(int i)
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{
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p = new int;
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std::cout << "new " << (void*)p << "\n";
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if (!p) {
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cout << "メモリ割り当てエラー\n";
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exit(1);
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}
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*p = i;
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}
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myclass::myclass(const myclass& ob)
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{
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p = new(nothrow) int;
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if (!p) {
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cout << "メモリ割り当てエラー\n";
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exit(1);
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}
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std::cout << "new " << (void*)p << "\n";
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*p = *ob.p;
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}
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int getval(myclass o)
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{
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std::cout << "getval\n";
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return *o.p; // 値を取得する
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}
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int main()
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{
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myclass a(1), b(2);
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cout << getval(a) << " " << getval(b);
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cout << "\n";
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cout << getval(a) << " " << getval(b);
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cout << "\n";
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return 0;
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}
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```
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実行結果:
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```
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new 000002324AA76DE0
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new 000002324AA76D40
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new 000002324AA76E80
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getval
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delete 000002324AA76E80
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1 new 000002324AA76E10
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getval
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delete 000002324AA76E10
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153
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2
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new 000002324AA76DD0
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getval
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delete 000002324AA76DD0
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1 new 000002324AA76CF0
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getval
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delete 000002324AA76CF0
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2
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delete 000002324AA76D40
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170
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delete 000002324AA76DE0
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```
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getvalの前後でnew/deleteされてて、そのポインタ値は組になってます。
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178
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179
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つまり、getvalの直前でコピーを作り、直後でそのコピーを廃棄しています。
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180
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なので二重解放になりません。
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