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[英]C++ default constructor and POD questions when initializing a new object
[英]C++ default constructor, initializing pointer with new object
我有以下問題:在myClass中我想默認初始化一個指向yourClass的指針,帶有一個新的yourClass地址。 不幸的是,如果我想在任何一點刪除指針,我得到一個(核心轉儲)。
class myClass
{
protected:
yourClass * yc;
public:
myClass() { yc = new yourClass(); }
myClass(yourClass * tyc ) { delete yc; yc = tyc; }
~myClass() { delete yc; yc = NULL; }
void setMyClass (yourClass * tyc) { delete yc; yc = tyc; }
void print () { yc->print(); }
};
int main()
{
yourClass b (//parameter);
myClass * a = new myClass();
a->print();
a->setMyClass(&b)
a->print();
delete a;
return 0;
}
a的print()應該產生兩種不同的打印,取決於//參數。
我認為你的等級是yc; 而不是yourClass * yc,但我想知道它是否可行。
編輯:我以下面的方式重新編寫代碼,它的工作原理。 仍然看起來很復雜,聰明的指針看起來很有希望,我仍然沒有應用“三個規則”。 這里的代碼。 謝謝大家。
class myClass
{
protected:
yourClass * yc;
bool dynamic;
public:
myClass() { dynamic = true; yc = new yourClass (); }
myClass (yourClass * tyc )
{
// dynamic init (like default)
if (tyc == NULL ) { dynamic = true; yc = new yourClass (); }
// static use of yc
else { dynamic = false; yc = tyc; }
}
// because only if dynamic is true, we need to erase
~blu () { if (dynamic) { delete yc; dynamic = false; } }
void setMyClass(yourClass* tyc)
{
// leaving unchanged if new-stuff is NULL or like old-stuff
if ( tyc == yc || tyc == NULL ) return;
else // treating dynamic and static differently
{
if (dynamic) // if flag is set, must be deleted
{
delete yc; yc = tyc; dynamic = false;
}
else // must not be deleted, dynamic is still false
{
yc = tyc;
}
}
}
void print () { yc->print(); }
};
你違反了三條規則。
這也是災難的秘訣:
myClass(yourClass * tyc ) { delete yc; yc = tyc; }
如果tyc==yc
會怎么樣? 對。 不漂亮 :)
myClass(yourClass * tyc ) { if (yc!=tyc) { delete yc; yc = tyc; } }
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