Structure Padding in C

Code:

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struct student
{
      int a;
      char c;
}s1;

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Actual size of the above structure is 3 bytes(lets say int is 2 bytes).

Is the declaration of above structure is correct or not as I didn't add any padding bytes?
Is the structure padding the compiler dependent?

You should not add padding bytes, let the compiler deal with that. It will decide where to put the padding so that your variables are correctly aligned on 2, 4 or 8 byte boundaries depending on the compiler/OS you are working with.

BTW... if ints in your compiler actually are 2 bytes, you seriously need to look into updating. The code it produces won't run on a 64 bit operating system.

Thank u very much tater....

Quote:

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Originally Posted by karthik537

Is the declaration of above structure is correct or not as I didn't add any padding bytes?

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It's fine, you don't have to pad yourself unless you have a reason to do so.

Quote:

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Is the structure padding the compiler dependent?

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Yes. With most compilers, you can also ask for no padding. Eg, with gcc:

Code:

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struct student
{
      int a;
      char c;
      #pragma pack(1)
}s1;

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Will ensure the struct is exactly sizeof(int) + sizeof(char).