CMPSC 311 – File Input/Output & Systems Programming

Vocabulary flashcards covering key terms, functions, flags, and concepts from the CMPSC 311 lecture on file input/output and system programming.

Input/Output (I/O)

The process of moving bytes into or out of devices, files, networks, etc.

Buffered I/O

I/O in which the system temporarily stores extra data in memory, reducing device accesses and system calls.

Unbuffered I/O

I/O performed directly between user buffers and the device, e.g., read() and write(), without extra caching by the C library.

Blocking I/O

I/O in which a call waits until the read or write completes before returning.

Non-blocking I/O

I/O in which the call returns immediately even if the operation has not completed, possibly resulting in short reads/writes.

Asynchronous I/O

I/O issued through a separate API that returns immediately and later triggers a callback when the operation completes.

Short read/write

A read or write that completes with fewer bytes than requested when using non-blocking I/O.

STDIN

The default standard input stream for a program (file descriptor 0).

STDOUT

The default standard output stream for a program (file descriptor 1).

STDERR

The default standard error stream for a program (file descriptor 2).

I/O Redirection

Shell feature that routes program input/output to or from files using operators like < and >.

Pipe (|)

Shell construct that sends the STDOUT of one program directly to the STDIN of another.

libc

The C standard library providing core functionality such as stdio, memory, math, and system-interface wrappers.

Library call

A function provided by a language’s standard library, e.g., fopen(); executes in user space.

System call

A kernel-mediated function invoked via the OS, e.g., open(); enters kernel mode.

FILE structure (FILE*)

An opaque C library object that maintains state for buffered, high-level file I/O.

Stream

Another name for a FILE* object representing a sequence of bytes for input or output.

fopen()

C library call that opens a file and returns a FILE* stream pointer.

fopen mode "r"

Opens existing text file for reading, stream positioned at start.

fopen mode "w"

Creates or truncates a text file for writing, stream positioned at start.

fopen mode "a"

Opens (or creates) a file for appending; writes occur at end of file.

fscanf()

Formatted input function that reads data from a FILE* according to a format string.

fgets()

Reads a line (or up to size-1 chars) from a FILE* into a buffer, stopping at newline or EOF.

fprintf()

Formatted output function that writes data to a FILE* using printf-style formatting.

fputs()

Writes a null-terminated string to a FILE* without additional formatting.

fflush()

Forces any buffered write data to be sent to the OS or discards buffered read data.

fclose()

Closes a FILE* stream and frees associated resources (also flushes buffers).

open()

System call that opens/creates a file and returns an integer file descriptor.

O_RDONLY

open() flag specifying read-only access.

O_WRONLY

open() flag specifying write-only access.

O_RDWR

open() flag specifying both read and write access.

O_CREAT

open() option that creates the file if it does not exist.

O_EXCL

open() option that requires O_CREAT and fails if the file already exists.

O_TRUNC

open() option that truncates an existing file to zero length.

File descriptor

A non-negative integer index into a per-process kernel table identifying an open file or device.

read()

System call that copies up to count bytes from a file descriptor into a buffer and returns the bytes read.

write()

System call that copies count bytes from a buffer to a file descriptor and returns the bytes written.

close()

System call that releases a file descriptor and its table entry.

Discretionary Access Control

UNIX model where file owners set read, write, and execute permissions for user, group, and world.

UNIX permission bits (rwx)

Three-bit groups indicating read (r), write (w), and execute (x) rights for owner, group, and others.

S_IRUSR

Permission constant (00400) giving file owner read access when used in mode arguments.

Absolute path

File path starting from the filesystem root '/', e.g., /home/user/file.txt.

Relative path

File path specified relative to the current working directory, e.g., ./docs/report.txt.

stdio.h

C header that declares standard I/O functions like printf(), scanf(), fopen(), etc.

unistd.h

POSIX header declaring system calls such as read(), write(), close(), and many others.