Solving the problem of garbled read function

Today I wrote a C program with a code that reads from a file with read and then uses printf to display the contents of the read. However, the content of the read display is always garbled, and some of the content is duplicated. For what reason. After a while, the read function reads the content and does not add the end flag of the string to '/0 ' at the end of the read content, so the read-out is not a valid string, but to add a string terminator to the line.

Char buf[512];
while (size = Read (fd,buf,sizeof (BUF)-1)) > 0) {

Buf[size] = '/0 ';
printf ("%s", buf);


}

So there's no garbled characters.