Brad,

On Friday 11 February 2005 21:03, Brad Bourn wrote:

I have a fuction that takes a vector as a parameter.

I want to be able to have a default value so I'm not required to pass anything if I don't need to.

I pass vectors by reference because of some things I need to do with it that pointers don't do.

anyway

I can define my function like this

func(vector<unsigned int> foo = vector<unsigned int>());

and everthing is fine, however if I define like this,

func(vector<unsigned int>& foo = vector<unsigned int>());

This is the same problem as you would get if you declared the function func(vector<unsigned int>& foo); and then called it with func(vector<unsigned int>())

This is an error because 'vector<unsigned int>()' is a temporary and you can only pass temporaries to 'const' reference parameters. Your function must be declared func(const vector<unsigned int>& foo); OR func(vector<unsigned int> foo); to work with temporaries.

I get

error: invalid type `std::vector<unsigned int, std::allocator<unsigned int> >' for default argument to ` std::vector<unsigned int, std::allocator<unsigned int> >&'

I am running SuSE 9.1 2.6.5-7.145-default

This syntax works with Borland 6 windoze (disclaimer: no, not mine, co-worker's)

Easy to explain. The ability to pass temporaries to non-const reference parameters has been disallowed for years in standard C++. It is incredibly dangerours. Some compilers support it despite this!

Michael

On Saturday 12 February 2005 03:52 am, Michael Stevens wrote:

This is an error because 'vector<unsigned int>()' is a temporary and you can only pass temporaries to 'const' reference parameters. Your function must be declared func(const vector<unsigned int>& foo); OR func(vector<unsigned int> foo); to work with temporaries.

This does allow it to compile, however, once inside the function, I can't use the std::find function because STL doesn't seem to like const iterators...

here is the error I get /usr/include/g++/bits/stl_iterator.h: In constructor ` __gnu_cxx::__normal_iterator<_Iterator, _Container>::__normal_iterator(const __gnu_cxx::__normal_iterator<_Iter, _Container>&) [with _Iter = const unsigned int*, _Iterator = unsigned int*, _Container = std::vector<unsigned int, std::allocator<unsigned int> >]':

/usr/include/g++/bits/stl_iterator.h:598: error: invalid conversion from `const unsigned int* const' to `unsigned int*'

B-)