C++ – How to Compute Length of Array

arraysc++

I have a C++ array declared as mentioned below:

CString carray[] =
{
        "A",
        "B",
        "C",
        "D",
        "E"
}

I want to determine the length of carray at runtime. I am doing:

int iLength = sizeof(carray)/sizeof(CString);

Is this correct?

You can use the following function template. If you're using Boost, you can call boost::size.

template <typename T, std::size_t N>
std::size_t size(T (&)[N])
{
    return N;
}

int iLength = size(carray);

As others have already stated, however, you should prefer std::vector to C-style arrays.

If you mean a C-style array, then you can do something like:

int a[7];
std::cout << "Length of array = " << (sizeof(a)/sizeof(*a)) << std::endl;

This doesn't work on pointers (i.e. it won't work for either of the following):

int *p = new int[7];
std::cout << "Length of array = " << (sizeof(p)/sizeof(*p)) << std::endl;

or:

void func(int *p)
{
    std::cout << "Length of array = " << (sizeof(p)/sizeof(*p)) << std::endl;
}

int a[7];
func(a);

In C++, if you want this kind of behavior, then you should be using a container class; probably std::vector.