strncpy(buff,src,n);

#include "stdafx.h"
#include <string.h>

int main(int argc, char* argv[])
{
	char *src="qwert";
	char buff[256];
	int n=2;
	strncpy(buff,src,n);
	buff[n]='\0';
	printf("%s,%d\n",buff,strlen(buff));
	return 0;
}