Getting the length of an array. Compiler errors.

Question

I've tried:

template <typename T,unsigned S> 
unsigned getArraySize(const T (&v)[S]) { return S; } 

after Motti's answer https://mcmap.net/q/63572/-how-do-i-find-the-length-of-an-array

but I've got this message:

error C2265: '' : reference to a zero-sized array is illegal

What's wrong with my compiler?

I gave a look at this page: http://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/4b78bcef-4c33-42f1-a4c5-fb6f702ced0b/vs6-c-compile-error-using-getaddrinfo so I tried this solution:

template <typename T,unsigned S> 
unsigned getArraySize(const T v[S]) { return S; } 

this compiles, but when I try to use it:

double myX[2] = {7,3};
std::cout << getArraySize(myX) << std::endl; 

I get a compilation error:
error C2783: 'unsigned int __cdecl getArraySize(const T [])' : could not deduce template argument for 'S'

Beside changing the compiler, is there a workaround I can use to get the array's size?

Openmouthed

Use std::array. What is the error when you do getArraySize(myX) with the first definition? The error implies a zero length array, but your array myX obviously has more than zero elements. – Bothy

Can you post the code that is giving you C2265 for the first solution? – Bechtel

The first example should work... I literally copy/pasted it and ran it and it returned 2. What compiler do you have? – Sperling

Did you try this on a more recent msvc compiler? vc6 is at least a decade old. – Monodic

Your first version should work. Can you post an SSCCE? – Bruch

You might not pass a 'const T []', a 'const T [1]' should work. – Indiscipline

@Monodic More like 2 decades. 10 years ago, there was VS 2003. – Bechtel

@Bothy my company is using VC6, I think std::array has recently been added to the standard library. – Openmouthed

@Angew the first solution in an included header file gives the error (even if the template function is never called) i.e. there's no more code than these two lines – Openmouthed

@Monodic I'm pretty sure that on a more recent compiler it works, I'll try at home – Openmouthed

@Bruch my example is short, self contained, correct (according to most compilers) but of course cannot compile (that's the reason why I ask a question, isn't it)? :-) – Openmouthed

@Openmouthed It would have been easier to rule out other errors if you had posted something like the demo linked from my last comment. – Bruch

@Openmouthed I guess the only answer here is "update to a more recent compiler, or at least to one which at least pretends to care about the standard." VC++6 was never one for following the standard, especially with templates. Can't really blame it, it was released in the same year as the first C++ standard, but really is not a C++ compiler. – Bechtel

@Openmouthed If updating isn't an option for whatever reason, you'll just have to fallback to the old C method sizeof(array) / sizeof(array[0]) as a workaround. But don't worry! Macros can help here! :D – Monodic

These are my accepted answers -the only answer here is "update to a more recent compiler, -If updating isn't an option for whatever reason, you'll just have to fallback to the old C method. – Openmouthed

Answer 1

This could be a limitation of VC6, have you tried other compilers?

Sauder

Answer 2

but I've got this message:

error C2265: '' : reference to a zero-sized array is illegal

Arrays with zero size are illegal in C++.
So this probably means you tried with an array of zero size.

this compiles, but when I try to use it:

If you don't use it. Then the compiler is going to ignore a template (even if it has errors). This is because you can not always deduce if a template function is correct without knowing the types involved. So unless there is a call to a template function no error message will be generated.

template <typename T,unsigned S>
unsigned getArraySize(const T v[S]) { return S; }

This fails because you are not allowed to pass arrays as parameters (you can only pass references to arrays).

Camlet