C ++数组const char

Question

Hello I have this very simple function:

    void sample(int data[])
    {
         const int DataSize = data[sizeof(data)] // Last int in array contains data size
         int DataTable[DataSize] = {}; // error here must have a constant value
    }

How can i make an empty array table the size of my last int in array?

Answer 1

As Neil Kirk mentioned, raw array sizes must be compile-time constants. DataSize is not a compile-time constant, it's a run-time constant.

Use an std::vector , its size can be determined at run-time.

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Additionally, sizeof(data) returns the size of data in bytes , not the number of elements in it. You need to pass the size of data as a parameter to be able to use it inside the function.

void sample(int data[], int size)
{
     const int DataSize = data[size - 1];
     // size - 1 is the index of the last element in data.

     std::vector<int> DataTable(DataSize);
     // DataTable now contains DataSize ints, all initialized to 0.
}

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Or, you could just turn data into a vector too which would simplify things a lot:

void sample(const std::vector<int>& data) // Pass data as a const reference.
{
     const int DataSize = data.back();
     // The `back` function accesses the last element in a vector.
     ....
}