Something strength !!!!!!!

This is a discussion on Something strength !!!!!!! within the C Programming forums, part of the General Programming Boards category; Please look at following 'C' code : main() { char c1; int i1; char c2; printf("%u %u %u", &c1, &i1, ...

  1. #1
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    Something strength !!!!!!!

    Please look at following 'C' code :

    main()
    {
    char c1;
    int i1;
    char c2;

    printf("%u %u %u", &c1, &i1, &c2);
    }


    I got output of the above mentioned code is :

    65497 65498 65501


    Here the difference between first two numbers is 1 and it is ok as the size of char type is 1. But I want to know why the difference between 2nd and 3rd number is 3, while the size of int data type is only 2. So acording to me the output shoud be as follows:

    65497 65498 65500

    Can anybody please tell me why this happens ?

    Thanking You,
    Chintan R Naik

  2. #2
    Banned master5001's Avatar
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    Sometimes your compiler is making an attempt at being smart and tries to optimize data along 32-bit boundaries. Though I don't believe that to be the case here. To be perfectly frank, if I wanted to know exactly where c1, i1, and c2 were in relation to each other in the frame I'd write the function in assembler. Trust your compiler's judgement in this area. I haven't seen too many instances where the compiler's output assembler is off in a way that will cost you performance.

  3. #3
    Been here, done that.
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    16 bit compiler? DOS? Probably one or both.
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    >16 bit compiler? DOS? Probably one or both.

    No.....I have ran this program fragment on 32-bit computer running on Windows'98.
    Chintan R Naik

  5. #5
    Cat
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    Yes, but was it COMPILED for a 32 bit computer? 16-bit code will still run.

    And it seems certain you didn't compile it for 32 bits -- an int should typically be 4 bytes under most popular 32 bit implementations. We know the final character variable can't overlap the integer, so the int must have a size of 2 bytes (or 3, but I am not aware of any compilers out there which would use a 3-byte integer type; certainly no x86 compilers).

    It seems obvious it was compiled as a 16-bit program. And it really doesn't matter where the compiler chooses to put things into memory -- the compiler gets to put them anywhere it feels like.

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    >And it really doesn't matter where the compiler chooses to put >things into memory -- the compiler gets to put them anywhere it >feels like.

    Do you mean that the efficiency factor particulary for memory allocation is completley depend on compiler.

    Pl. look at following two code fragments: Suppose both are running on 16 bit computer and also compiled for 16 bit.

    1.
    main()
    {
    int i;
    char c;

    printf("%c %d",c,i);
    }

    2.
    main()
    {
    char c;
    int i;

    printf("%c %d",c,i);
    }

    What I am thinking is first one will execute faster than second one. Faster by 1 instuction cycle. because according to me both are assiged at access boundary.

    Now if allocation is depend completly on compiler then I think we don't have to look at this point..... is it ok ???
    Chintan R Naik

  7. #7
    ATH0 quzah's Avatar
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    There is no point in optimizing most code. If you really need to, use the compiler flags which do so. Other than that, use a profiler on it to see where your bottlenecks are and rethink your algos. It's pointless to optimize "Hello World!".

    Quzah.
    Hope is the first step on the road to disappointment.

  8. #8
    zsaniK Kinasz's Avatar
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    Every cycle counts, if you loop 8,000,000,000 times at some point then it will make a minute difference if you have three or four extra cycles in each loop

    I'm newer to c than I am to assembly but i dont think just because your programming higher level for faster processors that you can say there is no point optimizing code
    "Assumptions are the mother of all **** ups!"

  9. #9
    the hat of redundancy hat nvoigt's Avatar
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    Quzah's point is that you should first find out where and what to optimize before starting to throw in wild optimization guesses.
    hth
    -nv

    She was so Blonde, she spent 20 minutes looking at the orange juice can because it said "Concentrate."

    When in doubt, read the FAQ.
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    Kinasz, you are right.....but I was thinking in this way because I think it is required at core level. Suppose in future I will get some microcontroller based work or some embedded system based work which is of my interest (though I haven't any experience yet towards this side), then I think knowlege about this type of technics will be very helpfull
    Chintan R Naik

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