itoa in C++

This is a discussion on itoa in C++ within the C++ Programming forums, part of the General Programming Boards category; What is the best way to implement IOTA in CPP ? Using CPP Standards? Given the following...I'd like to return ...

  1. #1
    Registered User Dave++'s Avatar
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    What is the best way to implement IOTA in CPP ? Using CPP Standards?

    Given the following...I'd like to return a character version of a library call.
    Code:
    std::string afunctionthatcallsanunchangableLib(){
         returnstring = convertitsimple(somelibraryfunc());
         return(returnstring);
    }
    Thanks,
    Dave

    <<split from http://cboard.cprogramming.com/showthread.php?t=86470>>
    Last edited by Dave_Sinkula; 06-17-2007 at 03:53 PM. Reason: better explaination <<split thread>>

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    Registered User Dave++'s Avatar
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    Also,
    This code...could it be made to work with integers easily?
    I am trying to go from an integer to binary to a string.

    http://faq.cprogramming.com/cgi-bin/...&id=1044780608

    Regards,
    Dave

    to Sinkula:
    thanks for the link...can you help with a better understanding of the overloading operator?
    Code:
    inline double convertToDouble(const std::string& s)
     {
       std::istringstream i(s);
       double x;
       if (!(i >> x))
         throw BadConversion("convertToDouble(\"" + s + "\")");
       return x;
     }
    and in
    Code:
    template <typename T>
    T rev_bits ( T val )
    {
      T ret = 0;
      unsigned int n_bits = sizeof ( val ) * CHAR_BIT;
    
      for ( unsigned i = 0; i < n_bits; ++i ) {
        ret = ( ret << 1 ) | ( val & 1 );
        val >>= 1;
      }
    
      return ret;
    }
    Last edited by Dave++; 06-17-2007 at 04:30 PM. Reason: added examples

  4. #4
    Dr Dipshi++ mike_g's Avatar
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    If you want to get a the binary value of an integer, as a string:
    Code:
    #include <stdio.h>
    #define size 100
    
    void DecToBin(int num, char *str)
    {
        short num_bits = 32;    
        short start=0; 
        short i, bit;
        
        for(i=num_bits-1; i>=0; i--)
        {
            bit=(num>>i) & 1;   
            if(start == 0) if(bit != 0) start=1;       
            if(start != 0)
            {    
                str[start-1]=bit+'0';
                if((i%8) == 0)
                {    
                     str[start]=' ';
                     start++;
                }
                start++;
            }  
        }  
        str[start-1]='\0';          
    }      
    
    int main()
    {
        int num;
        char binstring[size];
        printf("Enter a whole number: ");
        scanf("%i", &num);
        DecToBin(num, binstring);
        printf("%s", binstring);      
        getchar(), getchar();
    }

  5. #5
    Kiss the monkey. CodeMonkey's Avatar
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    You could always use a bitset, too, but that might be overkill.
    Last edited by CodeMonkey; 06-18-2007 at 10:26 PM. Reason: wrong class
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  6. #6
    Registered User
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    >> If you want to get a the binary value of an integer, as a string:
    Use std::bitset rather than coding a long implementation yourself.

    >> can you help with a better understanding of the overloading operator?
    Which overloaded operator?

    Also note that if you have boost, then lexical_cast is preferable to your own version (like the example from the FAQ Dave_Sinkula linked to).

  7. #7
    Registered User Dave++'s Avatar
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    Mike,
    Thanks for the code. I ran it on my end with no problems and it will integrate well into my application.

    dave.thanks(10^6);
    PS: found an error...won't work for zero
    So added this at the very begining (other mods were made to handle the early return)
    Code:
      if(num == 0){
         str[0]='0';
         str[1]='\0';
         return(str);
      }
    Daved,
    > Which overloaded operator?
    I don't know what this is saying.
    val >>= 1;
    Last edited by Dave++; 06-18-2007 at 07:38 PM. Reason: updates and learning

  8. #8
    The larch
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    It left-shifts val by one 1 bit and assigns the result to val (as any operator combined with = does). In mathematical terms that would be the equivalent of dividing by 2 (for unsigned integers).

    As to overloading is concerned: you have probably met the >> operator with cin. Well, there it has been overloaded to be an insertion operator, but originally it is a bitwise operator.
    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
    Deathray Engineer MacGyver's Avatar
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    Right shift, not left shift.

    In addition, there are two different types of shifts:

    1. Logical
    2. Arithmetic


    Logical is what when you want the entire number to be shifted over and treated as an unsigned number. Arithmetic is used when you want to keep the sign bit in place and preserve the overall "signess" or the number. The x86 processor has two instructions for each kind of shift, obviously one left and one right.

    In C and C++, the decision to shift logically vs arithmetically is determined by whether or not the number to be shifted is signed or unsigned. Down at the assembly and hardware level, there is no such thing as signed and unsigned numbers except what the programmer does to interpret and use them as such.
    Last edited by MacGyver; 06-19-2007 at 01:18 AM.

  10. #10
    Registered User Dave++'s Avatar
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    > but originally it is a bitwise operator

    Thanks to all.

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