memset() - question of using.

This is a discussion on memset() - question of using. within the C++ Programming forums, part of the General Programming Boards category; Hi, I want to fill up an array of int with 1. I have such problem: Code: #include <cstring> #include ...

  1. #1
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    memset() - question of using.

    Hi,
    I want to fill up an array of int with 1. I have such problem:
    Code:
    #include <cstring>
    #include <cstdio>
    
    int     main()
    {
            int     y[4]={9,9,9,9},
                    i;
            memset(y,1,4 * sizeof(int));
            for(i=0;i<4;i++)
                    printf("%d",y[i]);
            return 0;
    }
    and when i run it:
    $ ./a.out
    16843009168430091684300916843009$
    I have no clue what's wrong, I expect something with third argument of memset() but 4 * sizeof(int) is a size of y. Can anyone help me ?
    Regards.

  2. #2
    and the hat of wrongness Salem's Avatar
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    Because the 1 fills each byte, not each int.
    Each int is now 0x01010101 (which is some large number, probably the one you're seeing)
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
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    Hm... so how shouid i call memset?
    Regards.

  4. #4
    Super Moderator VirtualAce's Avatar
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    This will fix your problem:

    Code:
    void memset32(void *Buffer,DWORD value,DWORD size)
    {
      asm {
        les    edi,[Buffer]
        mov  ecx,[value]
        mov  eax,[size]
        rep   stosd
        and  ecx,03h
        rep   stosb
      }
    }

  5. #5
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    tx Bubba but is there no way to use standard memset? Btw. is this asm code portable, I mean if it depends on arch?
    Regards

  6. #6
    and the hat of wrongness Salem's Avatar
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    If you want to set something other than bytes, then use a for loop
    Code:
    for(i=0;i<4;i++) y[i] = 1;
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  7. #7
    Registered User hk_mp5kpdw's Avatar
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    Code:
    #include <algorithm>
    
    int y[4];
    
    std::fill(y,y+4,1); // Set all 4 elements of array "y" to 1
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  8. #8
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    Ok, now i have no doubt. Thank you.
    Regards.

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