string copy

Requirements: Write a function that implements a string copy function similar to strcpy. The prototype is defined as char *mystrcpy(char *dest, char *src). The function is to copy the string pointed to by src to the array pointed to by dest, and return the dest pointer. (Hint: the areas pointed to by src and dest may overlap).

Simple version number:

char * mystrcpy (char * dest, char * src)
{
	char * p = dest;
	while(*src != '\0'){
		* dest ++ = * src ++;
	}
	return p;
}

Storage space analysis:

The above case does not consider the problem of overlapping memory regions. There is also no validity check for input parameters.

The revised version number is:

char * mystrcpy (char * dest, char * src)
{
	char *d = dest;//input parameter backup
	char *s = src;
	
	int count = 0;
	
	assert(dest);//Pointer validity check
	assert(src);
	
	if(src == dest){
		return src;
	}
	count = strlen(src) + 1;
	if(count<=1){
		return 0;
	}
	if(dest < src || dest >= (src + count)){
		while(count--){
			*d++ = *s++;
		}
	}
	else{
		d = dest + count;
		s = src + count;
		while(count--){
			*d-- =*s--;
		}
	}
	return dest;
}