Array[n] vs Array[10] - Initializing array with va

问题:

I am having the following issue with my code:

int n = 10;
double tenorData[n]   =   {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

Returns the following error:

error: variable-sized object \'tenorData\' may not be initialized

Whereas using double tenorData[10] works.

Anyone know why?

回答1:

In C++, variable length arrays are not legal. G++ allows this as an \"extension\" (because C allows it), so in G++ (without being -pedantic about following the C++ standard), you can do:

int n = 10;
double a[n]; // Legal in g++ (with extensions), illegal in proper C++

If you want a \"variable length array\" (better called a \"dynamically sized array\" in C++, since proper variable length arrays aren\'t allowed), you either have to dynamically allocate memory yourself:

int n = 10;
double* a = new double[n]; // Don\'t forget to delete [] a; when you\'re done!

Or, better yet, use a standard container:

int n = 10;
std::vector<double> a(n); // Don\'t forget to #include <vector>

If you still want a proper array, you can use a constant, not a variable, when creating it:

const int n = 10;
double a[n]; // now valid, since n isn\'t a variable (it\'s a compile time constant)

Similarly, if you want to get the size from a function in C++11, you can use a constexpr:

constexpr int n()
{
    return 10;
}

double a[n()]; // n() is a compile time constant expression