memory - Stackalloc Pointer to Pointer in C# -

i have structue in c#:

[structlayout(layoutkind.sequential)] public unsafe struct svm_node {     internal int index;     internal double value; }

and wrote below code allocate unmanaged memory variable p

svm_node** p = stackalloc svm_node*[100];

but after executing code variable p null, if use code:

svm_node* p = stackalloc svm_node[100];

p real pointer. problem?

Deter