永久更改指针类型

Question

我需要知道是否实际上有一种方法可以轻松完成此操作。这只是我想要做一个例子...

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; 

因为PTR是一个void *，反正是有，我可以临时更改PTR的类型，所以我没有丢每次使用它？

我不能只创建另一个类型为Foo的指针，因为ptr在其他地方使用，并且需要是void类型。所以我想，暂时把它的类型Foo，以避免我不得不做的所有凌乱的演员。

**似乎有些人感到困惑......因为在程序中它的使用这样的PTR必须保持void类型： -

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必须保持void类型。我只是想知道是否有暂时的方式将ptr投射到另一种类型，所以请避免投射...

Answer 1

我不明白你为什么不能创建一个临时指针：

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 

有时候我用：

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

编辑：此答案已过时，因为原始问题已被修改。

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;