Accessing UNIX file system files

When accessing UNIX file system files, you should review the following considerations:

Use fread() instead of fgets(), and fwrite() in place of fputs(), wherever possible.
Use putc() instead of fputc(), and getc() instead of fgetc(), if you must write or read a character.
When using fflush(), beware of NULL file pointers; fflush(NULL) flushes all open streams.
Changing the buffer size for access to UNIX file system may provide advantages. Rather than using the default of 4K, you may want to use the setvbuf() function to set the buffer size to be the length of the read or write operation that you normally do.
For example, in applications that access files in a z/OS File System (zFS) file system, the recommended setvbuf() buffer size is 64K.

When you include the header file stdio.h, macros are defined for getc(), putc(), getchar(), and putchar(). To use the function calls instead of the macro calls, use #undef after the stdio.h header file is included. If you are working with a threaded application, these macros are automatically undefined forcing the application to use function calls, which are thread safe. The feature test macro _ALL_SOURCE causes these four macros to be undefined. However, if you require _ALL_SOURCE, and want these macros to be used in a non multi-threaded application, you can use feature test macro _ALL_SOURCE_NOTHREADS.