从 unsigned char * 到 unsigned int 的 memcpy

memcpy from unsigned char * to unsigned int

我不确定以下 C++ 代码的作用(我已经用点替换了无关紧要的部分):

unsigned char* p = ...;
unsigned int metaNum;
memcpy( &metaNum, p, sizeof( unsigned int ) );
p += sizeof( unsigned int );

for ( unsigned int m = 0; m < metaNum; m++ ) {

...

}

我知道memcpy

The underlying type of the objects pointed to by both the source and destination pointers are irrelevant for this function; The result is a binary copy of the data.

我仍然不确定 metaNum 的解释是什么。它是显而易见的还是与实施有关?

这不是特定于实现的:metaNum 被解释为 sizeof(unsigned int) 字节的序列,p 指向的相同字节数的内容被复制到其中.

这里唯一起作用的是 endianness: the same sequence of bytes copied into metaNum will be interpreted differently depending on how the hardware is storing multi-byte values, such as unsigned int. If the sequence comes from the same hardware, interpretation would be the same. Otherwise, you would need to use ntoh/hton 将字节序列调整为正确顺序的函数。