为什么在没有复制数据的情况下标准C库中没有像realloc()这样的函数? [英] Why is there no function in standard C library like realloc() without data copying?

问题描述

例如，我想要这样的功能:

For example, I want such a function:

char *dst = (char*)malloc(512);
char *src = (char*)malloc(1024);
...
dst = (char*)realloc(dst, 1024);
memcpy(dst, src, 1024);

如您所见，我只希望函数realloc()扩展缓冲区的大小，但是C库中的realloc()可能会从旧地址复制数据.那么像我想要的任何库中都有一个函数吗?

As you see, I just want the function realloc() to extend the size of buffer, but the realloc() in C library may copy data from old address. So is there a function in any library like what I want?

推荐答案

realloc尝试在不复制的情况下扩展了缓冲区，但是只有在多余的空间可用的情况下才能这样做.

realloc attempts do extend the buffer without copying, but can only do that if the extra space is free.

在您的情况下，您只是为src分配了空间，而该内存块可能已经使用了realloc所需的空间.在这种情况下，它只能在其他地方分配更大的块，然后将数据复制到该块.

In your case, you just allocated space for src and that memory block just might have used the space realloc would have needed. In that case it can only allocate a larger block somewhere else and copy the data to that block.

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