当打印到stdout并写入文件时，C字符串中的垃圾值

I'm playing around with C strings and streams to get a better understanding of them. I have this test program to read a fixed size block of data from an input file to a buffer, store the buffer contents in an intermediate storage (in this case, I want the storage to be able to store three different "reads") and then write the read string and one of the strings in intermediate storage to an output file.I'm playing around with C strings and streams t