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| <h2 class="chapter">13 Low-Level Input/Output</h2> |
| |
| <p>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 <a href="I_002fO-on-Streams.html#I_002fO-on-Streams">I/O on Streams</a>, as |
| well as functions for performing low-level control operations for which |
| there are no equivalents on streams. |
| |
| <p>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: |
| |
| <ul> |
| <li>For reading binary files in large chunks. |
| |
| <li>For reading an entire file into core before parsing it. |
| |
| <li>To perform operations other than data transfer, which can only be done |
| with a descriptor. (You can use <code>fileno</code> to get the descriptor |
| corresponding to a stream.) |
| |
| <li>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.) |
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| <li><a accesskey="1" href="Opening-and-Closing-Files.html#Opening-and-Closing-Files">Opening and Closing Files</a>: How to open and close file |
| descriptors. |
| <li><a accesskey="2" href="I_002fO-Primitives.html#I_002fO-Primitives">I/O Primitives</a>: Reading and writing data. |
| <li><a accesskey="3" href="File-Position-Primitive.html#File-Position-Primitive">File Position Primitive</a>: Setting a descriptor's file |
| position. |
| <li><a accesskey="4" href="Descriptors-and-Streams.html#Descriptors-and-Streams">Descriptors and Streams</a>: Converting descriptor to stream |
| or vice-versa. |
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| descriptors and streams. |
| <li><a accesskey="6" href="Scatter_002dGather.html#Scatter_002dGather">Scatter-Gather</a>: Fast I/O to discontinuous buffers. |
| <li><a accesskey="7" href="Memory_002dmapped-I_002fO.html#Memory_002dmapped-I_002fO">Memory-mapped I/O</a>: Using files like memory. |
| <li><a accesskey="8" href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>: How to check for input or output |
| on multiple file descriptors. |
| <li><a accesskey="9" href="Synchronizing-I_002fO.html#Synchronizing-I_002fO">Synchronizing I/O</a>: Making sure all I/O actions completed. |
| <li><a href="Asynchronous-I_002fO.html#Asynchronous-I_002fO">Asynchronous I/O</a>: Perform I/O in parallel. |
| <li><a href="Control-Operations.html#Control-Operations">Control Operations</a>: Various other operations on file |
| descriptors. |
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| file descriptors. |
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| flags associated with file |
| descriptors. |
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| flags associated with open files. |
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| file locking. |
| <li><a href="Interrupt-Input.html#Interrupt-Input">Interrupt Input</a>: Getting an asynchronous signal when |
| input arrives. |
| <li><a href="IOCTLs.html#IOCTLs">IOCTLs</a>: Generic I/O Control operations. |
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