sizeof struct

This is a discussion on sizeof struct within the C++ Programming forums, part of the General Programming Boards category; I'm running the following prog : Code: #include <iostream> using namespace std; struct customer { short number; // 1: int ...

  1. #1
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    sizeof struct

    I'm running the following prog :

    Code:
    #include <iostream>
    
    using namespace std;
    
    struct customer {
        short number;       //   1:
        int postcode;         //   2:
    };
    
    int main() {
    
        cout<<sizeof(customer)<<endl;
    
    }
    If I run it with line 1 in comments the output is 4.OK for that.
    If I run it with line 2 in comments the output is 2.OK for that too.
    But if i run it as it is above the outout is 8.Why is that?

    Thank you in advance.

  2. #2
    S Sang-drax's Avatar
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    Because the compiler belives that aligning structs to 4- or 8-byte boundaries will make your program faster.
    Last edited by Sang-drax : Tomorrow at 02:21 AM. Reason: Time travelling

  3. #3
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    "Because the compiler belives that aligning structs to 4- or 8-byte boundaries will make your program faster."


    ???
    That doesn't explain why sizeof (customer) will return 2 if there is only 1 short int, or 6 if there are 3 short ints (and no ints), yet if there are 3 short ints plus 1 int, it returns 12.

    Does it align structs that way only when they contain ints?

  4. #4
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