How is \0 incorporated into normal text files in reference to fgets

Question

I was just wondering that when you input text just using a normal application such as textedit (on OSX) would it still harbour the same '\0' character on the end of each string so that when read through fgets() if would pick said character up and stop reading?

Because I've created a normal text file, but fgets() keeps on stopping at the end of the designated length, instead of when it finds that character, so I have suspicious if it actually exists when I write to a normal text file.

For Example:

How Are You
There

fgets(str, 15, stdin); This would end up producing: TherAre You

Answer 1

No, text files don't generally contain any control characters. The termination is a C "feature", i.e. a property of how the C language and environment works with strings. Text files are independent of C. The termination is added (to the in-memory buffer into which the data has been read) by the fgets() function.

Answer 2

No, in general, text files do not contain \0 characters. fgets reads the number of characters requested, or to the end of the line, whichever comes first. It's fgets itself that appends the \0. From the man page:

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A terminating null byte ('\0') is stored after the last character in the buffer.

Answer 3

If your input file does contain a null byte and you're reading with fgets() or equivalent, you have difficulty knowing whether the null in the middle of the string was simply a null in the 'text' file or indicates that the last line of the file did not end with a newline, or that the line was truncated. Clearly, if you try another read and get more data, it was not a premature EOF. If the character immediately before the null byte is a newline, then you can assume that the null byte is the end of string marker added by fgets().

Generally speaking, therefore, if the file contains null bytes, it is not a good idea to use fgets() to read the file.