Temporaries passed to constructor yield invalid member references
in [C++]
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From: Martin B. on 1 Jun 2010 02:58 Razvan Cojocaru wrote: >> Use a const pointer. Use it for the argument passing and if it's not too >> much hassle also use it for the member. >> >> Bottom line for me is: Always use pointers for these parameters. >> Use a pointer member in "90%" of cases. > > I don't see the difference between his problem using a non-const He stated his problem as quote:"The problem is that the constructor allows passing temporaries (...)". > reference and what would ensue if he uses a const pointer (since a > reference is pretty much the functional equivalent of a const pointer, > dereferencing and checking for NULL aside). > Why did you snip the link I provided? It was discussed there. The difference is that you can pass a temporary as a const-ref without seeing it, while you cannot pass a temporary as a pointer without some syntactic overhead. (This statement does *only* apply to the immediate call - it does not apply to general lifetime management.) Example: A::A(int const& ref) : m_ref(ref) { } vs. B::B(int const* ptr) : m_ptr(ptr) // or m_ref(*ptr) { } void f() { int x; char y; A a1(x); // Fine, a1 can reference x from it's ref member A a2(y); // The ctor get's passed a temporary int object! // It does not reference y! A a3(42); // compiles just fine, will reference a temp! B b1(&x); // ok B b2(&y); // good: compiler error, because char* <> int* B b3(&42); // good: compiler error } Refs and Ptrs are functionally equivalent, I agree. They are absolutely not treated equivalent by the compiler+lang rules though. br, Martin -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
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