Create Array size Question

Hi everybody,

how can i create empty array? That means I want to create a array variable without specify the size of the array.
In my program, I wrote:

n1 = q - p + 1;
n2 = r - q;

int L[n1], R[n2];

Unfortunately, c++ only allow constant inside the bracket of the array.
I know it's possible in Java to write :
int L[]; So, can somebody tell me how to do that in c++?

Thanks

From Allen

You declare a pointer and use "new" to create the array at runtime

Like so

Code:

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#include <iostream>


int main(){

        int *ptr = 0;
        int p = 10,q = 50;
       
        int n1 = q - p + 1;
       
        ptr = new int[n1];
        if(!ptr){/*Error handling*/}
               
        for(int i = 0;i < n1;++i)
                ptr[i] = i * 2;
               
        for(int i = 0;i < n1;++i)
                std::cout << ptr[i] << " ";
       
        delete[] ptr;       
}

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Be Careful when using 'new'. It creates the memory allocations for the array in the heap, so if your heap isnt large enough the heap will begin getting inconsistent nodes and your application will likely crash. I also reccommend using calloc, malloc, and free. Or you could also just increase the size of the heap.

Quote:

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Originally posted by Xei
Be Careful when using 'new'. It creates the memory allocations for the array in the heap, so if your heap isnt large enough the heap will begin getting inconsistent nodes and your application will likely crash. I also reccommend using calloc, malloc, and free. Or you could also just increase the size of the heap.

---

:: Slaps forehead ::

calloc and malloc also use the heap - infact many implementations of new call malloc.....

The heap size recomended by your linker (assuming windows - linux may work differently) is usually enough........you have to be using an awful lot of memory for a heap to be too small