fgetc returns a strange character

I am reading input until EOF with fgetc(). I am running into a strange problem. Right before EOF, I am getting a char \337. I am not sure what that is.

Here is my code implementation:

char *get_file_paths() 
{
        char *return_str = NULL;
        int chars_read = 0;
        size_t buf_sz = 80;

        return_str = (char *) malloc(buf_sz * sizeof(char));

        while((*(return_str + chars_read) = fgetc(stdin)) != EOF) {
                chars_read++;
                if ((chars_read + 1) == buf_sz) {
                        buf_sz *= 2;
                        return_str = realloc(return_str, buf_sz);
                }
        }

        return return_str;

}

For instance, if I had a string :assignment_2/grepout.txt. I am getting the following when viewing return_str in gdb:

assignment_2/grepout.txt\n\337

I am really curious what that means. I looked online, but there is no mention of it. Could it be platform specific?

I am running the following version of gcc:

gcc version 4.8.1 20130909 [gcc-4_8-branch revision 202388] (SUSE Linux)

And I am running openSuse.