The memmove() function is used to copy a block of memory from one location to another, and it can handle overlapping blocks correctly. The function is declared in the string.h header file.

The syntax of the memmove() function is:

void *memmove(void *dest, const void *src, size_t n);

Here, dest is a pointer to the destination block of memory where the data is to be copied, src is a pointer to the source block of memory from where the data is to be copied, and n is the number of bytes to be copied.

The memmove() function returns a pointer to the destination block of memory (dest).

Note that the memmove() function is similar to the memcpy() function, but it can handle overlapping blocks correctly. If the blocks overlap and the direction of copying is such that the original data would be overwritten before it is copied, the memmove() function takes care to ensure that the data is copied correctly.