永久更改指針類型

Question

我需要知道是否實際上有一種方法可以輕鬆完成此操作。這只是我想要做一個例子...

void* ptr; 
ptr = new Foo; 
((Foo*)ptr)->member1 = some_val; 
((Foo*)ptr)->member2 = some_val; 
((Foo*)ptr)->member3 = some_val; 
((Foo*)ptr)->member4 = some_val; 
((Foo*)ptr)->member5 = some_val; 
((Foo*)ptr)->member6 = some_val; 

因爲PTR是一個void *，反正是有，我可以臨時更改PTR的類型，所以我沒有丟每次使用它？

我不能只創建另一個類型爲Foo的指針，因爲ptr在其他地方使用，並且需要是void類型。所以我想，暫時把它的類型Foo，以避免我不得不做的所有凌亂的演員。

**似乎有些人感到困惑......因爲在程序中它的使用這樣的PTR必須保持void類型： -

void* ptr; 
switch (bar) 
{ 
    case 1: 
     ptr = new Foo; 
     ((Foo*)ptr)->member1 = some_val; 
     ((Foo*)ptr)->member2 = some_val; 
     ((Foo*)ptr)->member3 = some_val; 
     ((Foo*)ptr)->member4 = some_val; 
     ((Foo*)ptr)->member5 = some_val; 
     ((Foo*)ptr)->member6 = some_val; 
    case 2: 
     ptr = new Doo; 
     ... 
    case 3: 
     ptr = new Scooby; 
     ... 

所以，PTR必須保持void類型。我只是想知道是否有暫時的方式將ptr投射到另一種類型，所以請避免投射...

Answer 1

我不明白你爲什麼不能創建一個臨時指針：

void* ptr; 
ptr = new Foo; 
{ 
Foo *pt=(Foo*)ptr; 
pt->member1 = some_val; 
pt->member2 = some_val; 
pt->member3 = some_val; 
pt->member4 = some_val; 
pt->member5 = some_val; 
pt->member6 = some_val; 
} 
void *t=ptr; // the original ptr 

有時候我用：

Foo &f= *((Foo*)ptr); 
f.member1 = some_val; 
f.member2 = some_val; 
f.member3 = some_val; 
f.member4 = some_val; 
f.member5 = some_val; 
f.member6 = some_val; 

Answer 2

編輯：此答案已過時，因爲原始問題已被修改。

您可以使用：

Foo* ptr; 

ptr = new Foo; 
ptr->member1 = some_val; 
ptr->member2 = some_val; 
ptr->member3 = some_val; 

或

void* ptrFromElseWhere; 
Foo* ptr = static_cast<Foo*>(ptrFromElseWhere); 

ptr->member1 = some_val; 
ptr->member2 = some_val; 
ptr->member3 = some_val;