size of binary string

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Thread: size of binary string

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  1. #1
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    size of binary string

    How to get the size of a binary string?
    length() and size() both stops at a \0 character.

    Code:
    // string::length
    #include <iostream>
    #include <string>
    using namespace std;
    
    int main ()
    {
      string str ("Tes\0t string");
      cout << "The length of str is " << str.length() << " characters.\n";
      cout << "The length of str is " << str.size() << " characters.\n";
      return 0;
    }
    Compiler MSVC++ 2013 with Code::Blocks.

  2. #2
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    Quote Originally Posted by Ducky View Post
    How to get the size of a binary string?
    length() and size() both stops at a \0 character.

    Code:
    // string::length
    #include <iostream>
    #include <string>
    using namespace std;
    
    int main ()
    {
      string str ("Tes\0t string");
      cout << "The length of str is " << str.length() << " characters.\n";
      cout << "The length of str is " << str.size() << " characters.\n";
      return 0;
    }
    Null-terminators don't belong in an std::string. What are you trying to do?



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  3. #3
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    I believe a string can handle binary strings just fine - including a 0 terminator. I'm not completely sure about this, and I think it's "nicer" to use a vector of chars for this, but that's a matter of opinion. Can those who actually know the C++ standard confirm binary strings are legal in the C++ standard (I'm actually 99.9% sure about this though)?

    Anyway, the problem with your code is that you use a C-string argument as constructor. And guess how it finds the length of that C-string? By finding a 0-terminator! But you can also pass another argument, being the number of characters in the character array, as such:
    Code:
    std::string test("x\x00ab", 4);
    That will create a string with 4 characters.

    And to others: what do you think is better for binary strings, vectors or strings, or does it not matter at all? And why do you think so?
    Last edited by EVOEx; 08-07-2010 at 09:59 AM.

  4. #4
    The larch
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    The character '\0' has no special meaning to std::string. The problem it is that it does have a special meaning for C-style strings which is what the argument is.

    I don't think I'd use a std::string for the storage of a binary string (e.g from a binary file).
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  5. #5
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    Ok, first of all thanks to all of you for your kind help!

    I have a function that returns a char* as a binary string of unknown size.
    Now i need to write this string to a file but for that first i need to know its size.

    First i tried to do it in C but then i thought it's maybe easier in C++.

    So maybe i should count it one by one by incrementing a pointer or use a vector?
    Last edited by Ducky; 08-07-2010 at 11:13 AM.
    Compiler MSVC++ 2013 with Code::Blocks.

  6. #6
    The larch
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    If your program returns a char* pointing to a buffer of unknown size, then there is nothing you can do.

    You have to keep the size around, and that's what a vector does.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  7. #7
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    Wouldnt this work to get the size?

    Code:
    char * binaryStr = RetBinStr(buffer);
    
    while (binaryStr--) { i++; }
    Compiler MSVC++ 2013 with Code::Blocks.

  8. #8
    The larch
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    So you think it will stop once the pointer reaches NULL and that is the size of the returned data?

    You can test your idea. I'd suppose the result is a crash sooner or later.

    ---

    Perhaps the function writes to the passed buffer and the return value points to the end of the range? Yes, in such a case, the length of the binary string would be:

    Code:
    char* end = RetBinStr(buffer);
    size_t length = end - buffer;
    If that is not so, you can't find out the size any more.
    Last edited by anon; 08-07-2010 at 12:03 PM.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  9. #9
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    That makes sense, thank you very much Anon!
    Compiler MSVC++ 2013 with Code::Blocks.

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