onnxruntime: What does "const auto elem_size = X->DataType()->Size()" mean for tensor X

[qingkun-fan]

For a tensor X;
we set "const auto elem_size = X->DataType()->Size()";
if datatype of tensor X is int32, so elem_size = 4;
if datatype of tensor X is int64, so elem_size = 8;
What if the data type of tensor X is std::string, what's value of elem_size???
Please help me! Thx!!!