上代码直接研究：

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int main()
{
        int *heap_d;
        int *heap_e;
        int *heap_f;
        heap_d = (int *)malloc(10);
        heap_e = (int *)malloc(10);
        printf("The d address is %p\n",heap_d);
        printf("The e address is %p\n",heap_e);
        free(heap_d);
        heap_d = NULL;
        heap_f = (int *)malloc(30);
        printf("The f address is %p\n",heap_f);
        return 0;
}
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输出：

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The d address is 0xf0d010 mem_d
The e address is 0xf0d030 mem_e
The f address is 0xf0d460 mem_f

可想而知，总共三段内存分配
mem_d|mem_e|
free
     |mem_e|
           |mem_f|
|xxxx|     |     |
xxx为无用内存，碎片，即使分配后已经free和置NULL操作。
越来越多的malloc使用，会促进内存碎片化加剧，最终内存不足。
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