在stm32开发可以调用c标准库的排序和查找 qsort bsearch

在嵌入式开发中，可以使用c标准库自带的库函数，而不用自己去早轮子，qsort 和bsearch就是其中的两个比较好用的

二分法查找，前提是已经排序好的数据。下面的代码， 如果数据为排序，则要进行排序后，再查找。

/* bsearch example */
#include <stdio.h>      /* printf */
#include <stdlib.h>     /* qsort, bsearch, NULL */

int compareints (const void *a, const void *b)
{
    return ( *(int *)a - * (int *)b );
}

int values[] = { 50, 20, 60, 40, 10, 30 };

int main ()
{
    int *pItem;
    int key = 45;
    qsort (values, 6, sizeof (int), compareints);
    pItem = (int *) bsearch (&key, values, 6, sizeof (int), compareints);
    if (pItem != NULL)
        printf ("%d is in the array.
", *pItem);
    else
        printf ("%d is not in the array.
", key);
    return 0;
}

快速排序

#include <stdio.h>
#include <stdlib.h>

int values[] = { 88, 56, 100, 2, 25 };

int cmpfunc (const void *a, const void *b)
{
    return ( *(int *)a - * (int *)b );  //升序
    //return ( *(int *)a - * (int *)b );  //降序
}

int main()
{
    int n;

    printf("排序之前的列表：
");
    for ( n = 0 ; n < 5; n++ )
    {
        printf("%d ", values[n]);
    }

    qsort(values, 5, sizeof(int), cmpfunc);

    printf("
排序之后的列表：
");
    for ( n = 0 ; n < 5; n++ )
    {
        printf("%d ", values[n]);
    }

    return (0);
}

比较函数需要特别注意~~~~

Pointer to a function that compares two elements.
This function is called repeatedly by qsort to compare two elements. It shall follow the following prototype:

int compar (const void* p1, const void* p2);

Taking two pointers as arguments (both converted to const void*). The function defines the order of the elements by returning (in a stable and transitive manner):

return value	meaning
<0	The element pointed to by p1 goes before the element pointed to by p2
0	The element pointed to by p1 is equivalent to the element pointed to by p2
>0	The element pointed to by p1 goes after the element pointed to by p2

For types that can be compared using regular relational operators, a general compar function may look like:
 

1 2 3 4 5 6

int compareMyType (const void * a, const void * b) { if ( *(MyType*)a < *(MyType*)b ) return -1; if ( *(MyType*)a == *(MyType*)b ) return 0; if ( *(MyType*)a > *(MyType*)b ) return 1; }