beginner needs help

This is a discussion on beginner needs help within the C Programming forums, part of the General Programming Boards category; hi, i'm new to C and need to no can anyone help with a small problem. wondering is it possible ...

  1. #1
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    beginner needs help

    hi, i'm new to C and need to no can anyone help with a small problem.
    wondering is it possible when im creating, a database system in C that can store information, can i make the information be stored alphabetically, and if so how do i go about it?

  2. #2
    B26354 Deckard's Avatar
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    633
    I suspect qsort() is what you want.
    Jason Deckard

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    how would i go about that? im pritty new to C and havent done qsort() before.

  4. #4
    Code Goddess Prelude's Avatar
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    This came up on a board search, it's a wonderful thing, technology.
    Code:
    void sortarray ( double array1[], int num ) 
    { 
      qsort ( array1, num, sizeof array1[0], cmp );
    }
    
    int cmp ( const void *x, const void *y )
    {
      if ( *(const double*)x < *(const double*)y )
        return -1;
      if ( *(const double*)x > *(const double*)y )
        return  1;
      return 0;
    }
    -Prelude
    My best code is written with the delete key.

  5. #5
    B26354 Deckard's Avatar
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    qsort() is found in stdlib.h. Its prototype is:
    Code:
    void qsort( void *base, size_t nel, size_t size, int (*compar)(const void *, const void *) );
    This may look intimidating, but it doesn't have to be. Let's take a look at each argument:
    • base - The memory address of the list of items to sort. If your entries are in an array, simply put the array name here.
      nel - The number of elements in your array.
      size - The size of each element in the array (not the size of the entire array).
      compar - The address of the function used to compare any two elements in your array.
    Assuming you are comparing strings, you may either use strcmp() as your compare function or encapsulate it in your own function:
    Code:
    int compare( void *a, void *b )
    {
      return ( strcmp(a,b) );
    }
    Here's a quick example:
    Code:
    #include <stdlib.h>
    #include <stdio.h>
    
    int compare( void *a, void *b )
    {
      return strcmp( a, b );
    }
    
    int main( void )
    {
      int i;
      char array[5][10] = { "One", "Two", "Three", "Four", "Five" };
    
      qsort( array, 5, 10, &compare );
    
      for ( i=0; i<5; i++ )
        printf( "%s\n", array[i] );
    
      return 0;
    }
    The output is:
    • Five
      Four
      One
      Three
      Two
    Jason Deckard

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