无符号数转字符串
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**源代码**

.. code-block:: c

    void ultoa(unsigned long num, char *str, char radix)
    {
        char index[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        int i = 0, j = 0, k = 0;

        do
        {
            str[i++] = index[num % radix];
            num /= radix;
        } while (num);
        char temp;
        for (j = k; j <= (i - 1) / 2; j++)
        {
            temp = str[j];
            str[j] = str[i - 1 + k - j];
            str[i - 1 + k - j] = temp;
        }
        str[i] = '\0';
    }



**例子**

.. code-block:: c

    char str_tmp[16] = {0};
    ultoa(322,str_tmp,10);