Do you know about the #pragma pack() in C++?

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This directive is used to specify diverse options to the compiler. These options are specific for the platform and the compiler you use. Consult the manual or the reference of your compiler for more information on the possible parameters that you can define with #pragma. If the compiler does not support a specific argument for #pragma, it is ignored — no error is generated.

The compiler, unless otherwise directed, will line up structure members on 2-byte or 4-byte boundaries — this makes it easier and faster for the processor to handle. Here, the structure contains secret padding bytes to make it happen. The pragma pack directive allows you to change this alignment scheme. Some things (particularly in relation to hardware and embedded programming such as robotics, telecommunication) do not have the luxury to waste bytes like this and they send their data in an exact fit. This means that it is not wise to read data from a hardware device directly into a normal structure. If you want to read data that is an exact fit into a structure — you can tell the compiler to make the structure an exact fit;

#pragma pack(push, 1) // exact fit - no padding
struct MyStruct
{
  char b; 
  int a; 
  int array[2];
};
#pragma pack(pop) //back to whatever the previous packing mode was

Without the pragma directive, the size of the structure is 16 bytes — with the packing of 1 — the size is 13 bytes.