使用memcpy时重叠的含义 [英] Meaning of overlapping when using memcpy

问题描述

我试图理解C库<string.h>

语法:void *memcpy(void*dst,const void*src,size_t n);

我知道此函数用于将指针src指向的内存内容复制到dst指针指向的位置，并返回dst指针指向的地址.

I know that this function is used to copy the contents of the memory pointed by pointer src to the location pointed by the dst pointer and return a address pointed by dst pointer.

我无法理解以下有关memcpy()的重要声明:

I am not able to understand the following important statement regarding memcpy():

• 使用memcpy()时，内存地址不应重叠，如果重叠，则memcpy()是不确定的.

• When using memcpy(), memory address should not overlap, if it overlaps then the memcpy() is undefined.

另一个查询是: 传递给函数第三个参数的值，即size_t n始终是整数值吗?

Another query is: Is the value passed to third argument of the function i.e size_t n is always an integer value?

推荐答案

根据评论，您的问题是您不了解重叠"是什么意思

From the comments your problem is that you don't understand what "overlapping" means:

重叠意味着:

这两个内存区域src和dst确实重叠:

Here the two memory regions src and dst do overlap:

但是在这里他们没有:

因此，如果您有重叠的内存区域，则不能使用memcpy，而必须使用memmove.

So if you have overlapping memory regions, then you cannot use memcpy but you have to use memmove.

第二个问题:

是的，size_t是无符号整数类型.第三个参数是要复制的字节数，因此除无符号整数类型外几乎没有其他内容.

Yes, size_t is an unsigned integer type. The third argument is the number of bytes to copy, so it can hardly be anything else than an unsigned integer type.

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