C语言标准库stdlib中qsort函数的使用

1，Syntax:

    #include 
    void qsort( void *buf, size_t num, size_t size, int (*compare)(const void*, const void *) );
2，qsort函数使用快速排序的方法，将buf中的数据按照compare定义的大小顺序进行排序。使用qsort前需要先定义compare函数。
3,例子：ACM， DNA Sorting
#include 

typedef struct
{
    char str[51];
    int measure;
} STRMEAS;

STRMEAS g_seq[100];
int N, M;

//Pay attention to prototype of this function.
int fun_com(const void* a, const void* b)
{
    STRMEAS *pa = (STRMEAS*) a;
    STRMEAS *pb = (STRMEAS*) b;
    return pa->measure - pb->measure;
}

fun_msr()
{
    int i, j, k, m, msr;
    char t;
    for (k = 0; k < M; ++ k)
    {
        msr = 0;
        STRMEAS sm;
        //Compute measure for each string.
        for (i = 0; i < N; ++ i)
        {
            sm = g_seq[k];
            t = sm.str[i];
            m = 0;
            for (j = i + 1; j < N; ++ j)
            {
                if (t > sm.str[j])
                    ++ m;
            }
            msr += m;
        }
        g_seq[k].measure = msr;
    }
}

main()
{
    int i;
    scanf("%d%d", &N, &M);
    for (i = 0; i < M; ++ i)
        scanf("%s", g_seq[i].str);
    fun_msr();
    qsort(g_seq, M, sizeof(STRMEAS), fun_com);
    for (i = 0; i < M; ++ i)
        printf("%s\n", g_seq[i].str);
}