Check if header is already included in TLC file.

I am using C-Mex S-function block and I have written .c and .tlc file for the block. The block needs a header file to be included when code is generated using embedded coder. If i use just one instance of the block, header file is included just once. But if I use multiple instances of the same block in the model then header file is included multiple times. How do i check in TLC if header file is already included?

I am using the following in my block tlc:

%function BlockTypeSetup(block, system) void
    %openfile buffer
    #include "MyHeader.h"
    %closefile buffer
    %<LibCacheIncludes(buffer)>
%endfunction %% BlockTypeSetup

Any help is greatly appreciated. Thanks.