Materials for Topic 5: Buffered File I/O

Full C Programs

• files.c - a C program using file pointers and calls to the following functions: fopen(), fprintf(), getc(), fgets(), and fclose().
• buffered_io.c - a C program using: fopen(), fwrite(), fread(), and fclose() to read a binary data from and write a binary data into a structure.

Runnable Linux Commands

Quick Links:

• gcc
• . ./.short_prompt
• . ./.long_prompt
• time
• dd bs=1 count=2097152
• dd bs=1024 count=2048
• stat
• xxd

• The command:
  gcc -Wall -Wextra -O2 -g -o program program.c
  compiles the C source code located inside the file program.c. See more details here.
• The command:
  . ./.short_prompt
  executes code inside a file named .short_prompt and sources it (applies all the changes to the current session.) See more details here.
• The command:
  . ./.long_prompt
  executes code inside a file named .long_prompt and sources it (applies all the changes to the current session.) See more details here.
• The command:
  time SomeCommand
  runs the command given by SomeCommand and, after the command finishes running, displays how much time the command executed, provided in terms of the (i) the elapsed real time between invocation and termination, (ii) the user CPU time, and (iii) the system CPU time.
• The command:
  dd bs=1 count=2097152 if=/dev/zero of=pirate1
  copies 2097152 blocks of size 1 byte each from the file at /dev/zero (which is a disk-like file providing an infinite stream of zeros, for testing and debugging purposes) to a file named pirate1.
• The command:
  dd bs=1024 count=2048 if=/dev/zero of=pirate2
  copies 2048 blocks of size 1024 bytes each from the file at /dev/zero (which is a disk-like file providing an infinite stream of zeros, for testing and debugging purposes) to a file named pirate2. Since disks process data in terms of blocks (which are usually multiples of 512,) we expect this call to run much faster than the call dd bs=1 count=2097152 if=/dev/zero of=pirate1.
• The command:
  stat fileOrDiskName
  shows some statistics about the file or disk given by fileOrDiskName. For example, stat /dev/sda shows some statistics about the disk sda. The context in which this command is mentioned in the lecture notes is that it lets you view the block size that the disk uses, such as 4K = 4096.
• The command:
  xxd myFile
  prints the contents of the file myFile in hexadecimal. A hexadecimal view allows you to understand what characters exist in the file, even if they are invisible in decimal (normal) view, such as null characters and other special ASCII characters.

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