I have some newbie questions

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  1. #1
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    Question I have some newbie questions

    Hello everyone!

    I am an experienced Pascal programmer but I'm new to C++. I'm trying to avoid asking stupid questions but every book, tutorial, FAQ, etc I have found always assumes that I know this stuff. Please help me if you can!

    1. What does the underscore (_) and double underscore (__) in front of a function and/or variable name mean?

    2. What is the difference (if any) between these two lines of code? I'm specifically talking about the placement of the *

    int Read(unsigned char *buff);
    int Read(unsigned char* buff);

    3. In the following function if the IF condition evaluates to true will that cause a memory leak with temp?

    int FileChunk::Read(unsigned char *buff,int maxNum)
    {
    DWORD numRead = 0;
    //allocate a buffer big enough to hold the users data plus the header
    unsigned char *temp = new unsigned char[maxNum + sizeof(cid)];

    //read in the specified number of bytes
    if (numRead = GenericFile::Read(temp,maxNum + sizeof(cid)))
    {
    ... //misc code

    //return the number of bytes read
    return numRead;
    }

    delete[] temp;

    //return false
    return 0;
    }



    I would appreciate any help you can provide. Thanks!

    Myra Mains

  2. #2
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    2. No difference at all. It is all a matter of style preference.

  3. #3
    Used Registerer jdinger's Avatar
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    Re: I have some newbie questions

    Welcome aboard, Myra...

    >>1. What does the underscore (_) and double underscore (__) in front of a function and/or variable name mean?

    It doesn't actually mean anything. Just a naming convention.

    >>2. What is the difference (if any) between these two lines of code? I'm specifically talking about the placement of the *

    >>int Read(unsigned char *buff);
    >>int Read(unsigned char* buff);

    They mean the same thing. Both mean that the function Read takes a param that is an unsigned char pointer called buff. The placement of the * is (more or less) a matter of your own style.

  4. #4
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    Re: I have some newbie questions

    Originally posted by Myra Mains

    1. What does the underscore (_) and double underscore (__) in front of a function and/or variable name mean?
    Can't say, never seen that.
    2. What is the difference (if any) between these two lines of code? I'm specifically talking about the placement of the *

    int Read(unsigned char *buff);
    int Read(unsigned char* buff);
    No difference, matter of preference.
    3. In the following function if the IF condition evaluates to true will that cause a memory leak with temp?

    int FileChunk::Read(unsigned char *buff,int maxNum)
    {
    DWORD numRead = 0;
    //allocate a buffer big enough to hold the users data plus the header
    unsigned char *temp = new unsigned char[maxNum + sizeof(cid)];

    //read in the specified number of bytes
    if (numRead = GenericFile::Read(temp,maxNum + sizeof(cid)))
    {
    ... //misc code

    //return the number of bytes read
    return numRead;
    }

    delete[] temp;

    //return false
    return 0;
    }
    Not for the reason you state, but you need another closing brace after delete[] temp.
    Truth is a malleable commodity - Dick Cheney

  5. #5
    and the hat of wrongness Salem's Avatar
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    1. All symbols with leading underscores are reserved names. You should never create a symbol in your own code which begins with an underscore.

  6. #6
    Used Registerer jdinger's Avatar
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    Ah! You do learn something new everyday. I never actually use an underscore in my own function/variable naming but I never knew that it is for reserved names.

    Sorry if my reply mislead anyone. Thanks for the save, Salem!

  7. #7
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    Actually I think the double underscores in most symbols (a.k.a __A_SYMBOL__) is used so it would be EXTREMELY unlikely that you would have a symbol with the same name, causing a compiler error.

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