Hard Coding Vectors question!

sorry about that c++ vector

I believe this is something that is being talked about for inclusion in the next c++ standard. So, with luck, it may be widely available 10 years from now [grin].

Right now there isn't much better than:

There's no real reason to hardcode a vector. I'm not making excuses to make up for C++'s lack of a way to do vector literals either :P

Just use an array. If you know the size already, why do you need a vector? A vector doesn't do much more than a vector (resizing being the key one). If you access your members through operator[], it doesn't do bounds checking either. Do you really need a vector? Are more elements going to be added to this collection?

rip-off's solution should work, but it's a little messy. Be careful with pointer arithmetic. Just make sure to make that array in a static scope. Either a global (or hidden in a namespace), a static in a function, or a static member variable. Make it const too!

There's also the Boost.Assignment library.


jfl.

Quote:

Original post by jonahrowley There's no real reason to hardcode a vector. I'm not making excuses to make up for C++'s lack of a way to do vector literals either :P Just use an array. If you know the size already, why do you need a vector? A vector doesn't do much more than a vector (resizing being the key one). If you access your members through operator[], it doesn't do bounds checking either. Do you really need a vector? Are more elements going to be added to this collection? rip-off's solution should work, but it's a little messy. Be careful with pointer arithmetic. Just make sure to make that array in a static scope. Either a global (or hidden in a namespace), a static in a function, or a static member variable. Make it const too!

The vector will copy the contents of the array into itself, the array doesn't have to stick around.

A better option would be to have the data in a file, and load it into the vector. This can be quite easy, and is a much better alternative, given that you can change the data and not have to recompile your program.

And @jonahrowley:

Quote:

Do you really need a vector?

Do you lose anything by not using a vector? [grin]

To fit your object type, though. This isn't exactly what you're talking about (unless it is) but you get the idea.

Quote:

Original post by rip-off The vector will copy the contents of the array into itself, the array doesn't have to stick around.

My concern was performance. If this vector gets large and is a stack variable, not only are you allocating and populating an array, but copying all elements into a vector. Of course, it doesn't matter if both the array and vector are static variables.

The vetor object may be on the stack, but it's contents will be on the heap.

Write your own vector implementation, and overload the assignment operator?

Nah [grin]


C

Quote:

Original post by jflanglois There's also the Boost.Assignment library. jfl.

Yep. And if you want constant-sized arrays (there is good reason not to use a std::vector if you *don't* want the resize functionality: you improve documentation and express intent more clearly by saying "the container is supposed to have this fixed size because of X design reason") that still have object-like functionality/general niceness, look at Boost.Array.