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(libc.info)Low-Level I/O

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Low-Level Input/Output
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   This chapter describes functions for performing low-level
input/output operations on file descriptors.  These functions include
the primitives for the higher-level I/O functions described in Note:
I/O on Streams, as well as functions for performing low-level control
operations for which there are no equivalents on streams.

   Stream-level I/O is more flexible and usually more convenient;
therefore, programmers generally use the descriptor-level functions only
when necessary.  These are some of the usual reasons:

   * For reading binary files in large chunks.

   * For reading an entire file into core before parsing it.

   * To perform operations other than data transfer, which can only be
     done with a descriptor.  (You can use `fileno' to get the
     descriptor corresponding to a stream.)

   * To pass descriptors to a child process.  (The child can create its
     own stream to use a descriptor that it inherits, but cannot
     inherit a stream directly.)

Opening and Closing Files

How to open and close file

descriptors.

I/O Primitives

Reading and writing data.

File Position Primitive

Setting a descriptor's file

position.

Descriptors and Streams

Converting descriptor to stream

or vice-versa.

Stream/Descriptor Precautions

Precautions needed if you use both

descriptors and streams.

Scatter-Gather

Fast I/O to discontinuous buffers.

Memory-mapped I/O

Using files like memory.

Waiting for I/O

How to check for input or output

on multiple file descriptors.

Synchronizing I/O

Making sure all I/O actions completed.

Asynchronous I/O

Perform I/O in parallel.

Control Operations

Various other operations on file

descriptors.

Duplicating Descriptors

Fcntl commands for duplicating

file descriptors.

Descriptor Flags

Fcntl commands for manipulating

flags associated with file descriptors.

File Status Flags

Fcntl commands for manipulating

flags associated with open files.

File Locks

Fcntl commands for implementing

file locking.

Interrupt Input

Getting an asynchronous signal when

input arrives.

IOCTLs

Generic I/O Control operations.