从构造函数中抛出异常。 [英] throwing exception from constructor .
问题描述
我读过，常见问题解答：17.4]如果我的构造函数
可能会抛出异常，我应该如何处理资源？
上面常见问题解答说使用智能指针建设者。因为如果从构造函数抛出
异常，它的析构函数就不会运行。所以要求
避免使用内存lekage使用智能指针。
但是如果抛出异常，我们可以在catch块中释放资源。所以
使用智能指针不是必须的，我们有这个secnd选项。我是
对吗？
mangesh写道：我读过，常见问题解答：17.4]如果我的构造函数可能会抛出异常，我应该如何处理资源？
上面常见问题解答说在构造函数中使用智能指针。因为如果从构造函数抛出异常，它的析构函数就不会运行。所以要避免使用内存lekage使用智能指针。
但是如果抛出异常，我们可以释放catch块中的资源。
所以使用智能指针不是必须的，我们有这个secnd选项。我对吗？
你可以在一个catch块中释放，除非你忘记了资源
将被释放。如果它是构造体内的局部对象，
你怎么知道它在catch块中释放的价值？
V
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mangesh写道：我读过，常见问题：17.4]如果我的构造者如何处理资源
可能会抛出异常吗？
上面的faq说在构造函数中使用智能指针。因为如果从构造函数抛出异常，它的析构函数就不会运行。所以要避免使用内存lekage使用智能指针。
但是如果抛出异常，我们可以释放catch块中的资源。所以
使用智能指针不是必须的，我们有这个secnd选项。我对吗？
考虑：
class ResourceHolder {
int * pointer1;
int * pointer2;
//阻止复制和分配
ResourceHolder（const ResourceHolder&）;
ResourceHolder& operator =（const ResourceHolder&）;
public：
ResourceHolder（）：pointer1（new int（1）），pointer2（new int（2））{}
~ResourceHolder（）{
删除指针1;
删除指针2;
}
}
行：
ResourceHolder r;
需要分配2个整数，其中任何一个都可以失败并抛出
异常。问题是：哪一个失败了？
如果更改构造函数以包含try catch：
ResourceHolder（）：pointr1（0），pointer2（0 ）{
//如果这个抛出，那就没关系
pointer1 = new int（1）;
try {
//如果抛出，清理指针1
pointer2 = new int（2）;
} catch（）{
删除指针1;
}
}
这开始变得有点乱，想象一下5资源，
将RAII应用于所有资源更好，只需使用智能
指针，即使它只是std :: auto_ptr< int> ;.
它更不容易出错。
Ben Pope
-
我不只是一个数字。对于很多人来说，我被称为字符串...
我们不能在catch块中明确地调用析构函数吗？
I read , FAQ : 17.4] How should I handle resources if my constructors
may throw exceptions?
Above faq says that use smart pointer in construcors . Because if
exception is thrown from constructor it''s destructor is not run .So to
avoid memory lekage use smart pointer .
But if exception is thrown we can release resources in catch block . So
use of smart pointer is not must , we have this secnd option . Am i
right ?
mangesh wrote:I read , FAQ : 17.4] How should I handle resources if my constructors
may throw exceptions?
Above faq says that use smart pointer in construcors . Because if
exception is thrown from constructor it''s destructor is not run .So to
avoid memory lekage use smart pointer .
But if exception is thrown we can release resources in catch block .
So use of smart pointer is not must , we have this secnd option . Am i
right ?
You can release in a catch block, unless you lose track of the resource
to be released. If it''s a local object in the body of the construct,
how do you know its value to release in the catch block?
V
--
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mangesh wrote:I read , FAQ : 17.4] How should I handle resources if my constructors
may throw exceptions?
Above faq says that use smart pointer in construcors . Because if
exception is thrown from constructor it''s destructor is not run .So to
avoid memory lekage use smart pointer .
But if exception is thrown we can release resources in catch block . So
use of smart pointer is not must , we have this secnd option . Am i
right ?
Consider:
class ResourceHolder {
int* pointer1;
int* pointer2;
// prevent copy and assignment
ResourceHolder(const ResourceHolder&);
ResourceHolder& operator=(const ResourceHolder&);
public:
ResourceHolder() : pointer1(new int(1)), pointer2(new int(2)) {}
~ResourceHolder() {
delete pointer1;
delete pointer2;
}
}
The line:
ResourceHolder r;
Requires allocation of 2 ints, either of which could fail and throw an
exception. The problem is: which one failed?
If you change the constructor to include try catch:
ResourceHolder() : pointr1(0), pointer2(0) {
// if this throws, it''s ok
pointer1 = new int(1);
try {
// if this throws, clean up pointer 1
pointer2 = new int(2);
} catch () {
delete pointer1;
}
}
That''s starting to get a bit messy, imagine scaling that to 5 resources,
it''s better to apply RAII to all resources, and just use a smart
pointer, even if it''s just std::auto_ptr<int>.
It''s much less error prone.
Ben Pope
--
I''m not just a number. To many, I''m known as a string...
can''t we call destructor explicitly in catch block ?
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