如果指针C变更多少内存将被释放？ [英] How much memory would be freed if pointer is changed in C?
问题描述
假设有内存20块和一个指针 P 指向第一个块。
现在，当我做的：
Let's say there are 20 blocks of memory and a pointer p is pointing to the first block.
Now, when I do:
p++;
free(p);
如何记忆很多块将被释放，为什么？
How many blocks of memory would be freed and why?
推荐答案
取消确定性。不能说。您需要提供这是由返回）确切的指针的malloc（。
Un-deterministic. Cannot say. You need to supply the exact pointer which was returned by malloc().
指针传递到免费（）它不受返回的malloc（） [家庭]是< A HREF =https://en.wikipedia.org/wiki/Undefined_behavior>未定义行为。
Passing a pointer to free() which is not returned by malloc() [and family] is undefined behaviour.
根据你的问题，如果的malloc（） -ed指针存储在 P ，和你做点++ 并调用免费（p）; ，那么 p 是不再指向 按的的释放calloc ，的malloc 或的realloc 功能。
As per your question, if the malloc()-ed pointer is stored in p, and you do p++ and call free(p);, then there p is not anymore a pointer returned by the calloc, malloc, or realloc function.
按章节7.20.3.2， C99 标准，第二段
As per Chapter 7.20.3.2, c99 standard, 2nd paragraph
的自由功能使空间指向由ptr被解除分配，即，用于进一步分配可用。若ptr为空指针，不会发生任何操作。否则，如果该参数不匹配的释放calloc，malloc或realloc函数返回前面的指针，或者如果空间已被释放呼叫释放或realloc，该行为是不确定的。
The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by the calloc, malloc, or realloc function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined.
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