Re: Ideas for strong guarantee?
thiago.adams@gmail.com wrote:
I'm using exceptions to report errors in my code and I think that it
is a good idea. But in some circumstances is hard to implement a strong
guarantee for functions.
I would like suggestions for the code below:
class X {
std::vector<Type*> m_vec1;
std::vector<Type*> m_vec2;
void func()
{
Type * p1 = new Type();
Type * p2 = new Type();
m_vec1.push_back(p1);
m_vec2.push_back(p2);
}
};
// partial solution...
void func()
{
std::auto_ptr<Type> sp1(new Type());
std::auto_ptr<Type> sp2(new Type());
m_vec1.push_back(sp1.get()); //
sp1.release();
m_vec2.push_back(sp2.get()); //
sp2.release();
}
This solution is almost correct, but if some exceptions occurs at
second push_back I need to keep m_vec1 unchanged.
It can be solved by using scope guards. I find custom local guards most
flexible (compared to Alexandrescu's scope guard).
#include <vector>
int main()
{
std::vector<int*> a, b;
struct guard
{
std::vector<int*> *a, *b;
int *p, *q;
void release() { a = 0; b = 0; p = 0; q = 0; }
~guard()
{
if(a)
a->pop_back();
if(b)
b->pop_back();
delete p;
delete q;
}
} guard = {};
a.push_back(guard.p = new int(1));
guard.a = &a;
b.push_back(guard.q = new int(2));
guard.b = &b;
// more code that may throw
guard.release();
}
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