qsort - aid

This is a discussion on qsort - aid within the C++ Programming forums, part of the General Programming Boards category; Code: string *array; //dynmically allocated Code: qsort ((void*)array, nNum, sizeof (*array), compare ); Code: int compare(const void* string1, const void* ...

  1. #1
    eat my shorts!
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    qsort - aid

    Code:
    string *array;
    //dynmically allocated
    Code:
    qsort ((void*)array, nNum, sizeof (*array), compare );
    Code:
    int compare(const void* string1, const void* string2)
    {
      return stricmp ( (const char*)string1, (const char*)string2);
    }
    it is not sorting data. Could someone help me
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  2. #2
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    array is an array of std::string objects, not an array of char*. PROBABLY something like this (not compiled or tested):

    Code:
    qsort ((void*)array, nNum, sizeof (string), compare );
    Code:
    int compare(const void* string1, const void* string2)
    {
       std::string* s1 = (std::string*)string1;
       std::string* s2 = (std::string*)string2;
       
      return s1->compare(*s2);
    }

  3. #3
    Cat without Hat CornedBee's Avatar
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    Just use std::sort instead of qsort.

    Code:
    std::sort(array, array+size);
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  4. #4
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    You cannot cast a string to a const char*. If you want a const char* from a string, use the c_str() function.

    The other posted solutions don't do case-insensitive string compares, so while you should use sort, you will still have to create your own comparison function that uses stricmp.

  5. #5
    Cat without Hat CornedBee's Avatar
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    Wait, you want case-insensitive sorting, right? Give me a moment.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  6. #6
    eat my shorts!
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    Quote Originally Posted by Ancient Dragon
    array is an array of std::string objects, not an array of char*. PROBABLY something like this (not compiled or tested):

    Code:
    qsort ((void*)array, nNum, sizeof (string[0]), compare );
    Code:
    int compare(const void* string1, const void* string2)
    {
       std::string* s1 = (std::string*)string1;
       std::string* s2 = (std::string*)string2;
       
      return s1->compare(*s2);
    }
    it worked, thanks
    but could you explain the return line please?
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  7. #7
    Cat without Hat CornedBee's Avatar
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    There you go:
    Code:
    struct iless
    {
      bool operator()(std::string &lhs, std::string &rhs) {
        return stricmp(lhs.c_str(), rhs.c_str()) < 0;
      }
    };
    
    std::sort(array, array+size, iless());
    Personally I'd do it differently, but this code is clearer.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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