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| <h4 class="subsection">1.3.3 Reserved Names</h4> |
| |
| <p><a name="index-reserved-names-26"></a><a name="index-name-space-27"></a> |
| The names of all library types, macros, variables and functions that |
| come from the ISO C<!-- /@w --> standard are reserved unconditionally; your program |
| <strong>may not</strong> redefine these names. All other library names are |
| reserved if your program explicitly includes the header file that |
| defines or declares them. There are several reasons for these |
| restrictions: |
| |
| <ul> |
| <li>Other people reading your code could get very confused if you were using |
| a function named <code>exit</code> to do something completely different from |
| what the standard <code>exit</code> function does, for example. Preventing |
| this situation helps to make your programs easier to understand and |
| contributes to modularity and maintainability. |
| |
| <li>It avoids the possibility of a user accidentally redefining a library |
| function that is called by other library functions. If redefinition |
| were allowed, those other functions would not work properly. |
| |
| <li>It allows the compiler to do whatever special optimizations it pleases |
| on calls to these functions, without the possibility that they may have |
| been redefined by the user. Some library facilities, such as those for |
| dealing with variadic arguments (see <a href="Variadic-Functions.html#Variadic-Functions">Variadic Functions</a>) |
| and non-local exits (see <a href="Non_002dLocal-Exits.html#Non_002dLocal-Exits">Non-Local Exits</a>), actually require a |
| considerable amount of cooperation on the part of the C compiler, and |
| with respect to the implementation, it might be easier for the compiler |
| to treat these as built-in parts of the language. |
| </ul> |
| |
| <p>In addition to the names documented in this manual, reserved names |
| include all external identifiers (global functions and variables) that |
| begin with an underscore (‘<samp><span class="samp">_</span></samp>’) and all identifiers regardless of |
| use that begin with either two underscores or an underscore followed by |
| a capital letter are reserved names. This is so that the library and |
| header files can define functions, variables, and macros for internal |
| purposes without risk of conflict with names in user programs. |
| |
| <p>Some additional classes of identifier names are reserved for future |
| extensions to the C language or the POSIX.1 environment. While using these |
| names for your own purposes right now might not cause a problem, they do |
| raise the possibility of conflict with future versions of the C |
| or POSIX standards, so you should avoid these names. |
| |
| <ul> |
| <li>Names beginning with a capital ‘<samp><span class="samp">E</span></samp>’ followed a digit or uppercase |
| letter may be used for additional error code names. See <a href="Error-Reporting.html#Error-Reporting">Error Reporting</a>. |
| |
| <li>Names that begin with either ‘<samp><span class="samp">is</span></samp>’ or ‘<samp><span class="samp">to</span></samp>’ followed by a |
| lowercase letter may be used for additional character testing and |
| conversion functions. See <a href="Character-Handling.html#Character-Handling">Character Handling</a>. |
| |
| <li>Names that begin with ‘<samp><span class="samp">LC_</span></samp>’ followed by an uppercase letter may be |
| used for additional macros specifying locale attributes. |
| See <a href="Locales.html#Locales">Locales</a>. |
| |
| <li>Names of all existing mathematics functions (see <a href="Mathematics.html#Mathematics">Mathematics</a>) |
| suffixed with ‘<samp><span class="samp">f</span></samp>’ or ‘<samp><span class="samp">l</span></samp>’ are reserved for corresponding |
| functions that operate on <code>float</code> and <code>long double</code> arguments, |
| respectively. |
| |
| <li>Names that begin with ‘<samp><span class="samp">SIG</span></samp>’ followed by an uppercase letter are |
| reserved for additional signal names. See <a href="Standard-Signals.html#Standard-Signals">Standard Signals</a>. |
| |
| <li>Names that begin with ‘<samp><span class="samp">SIG_</span></samp>’ followed by an uppercase letter are |
| reserved for additional signal actions. See <a href="Basic-Signal-Handling.html#Basic-Signal-Handling">Basic Signal Handling</a>. |
| |
| <li>Names beginning with ‘<samp><span class="samp">str</span></samp>’, ‘<samp><span class="samp">mem</span></samp>’, or ‘<samp><span class="samp">wcs</span></samp>’ followed by a |
| lowercase letter are reserved for additional string and array functions. |
| See <a href="String-and-Array-Utilities.html#String-and-Array-Utilities">String and Array Utilities</a>. |
| |
| <li>Names that end with ‘<samp><span class="samp">_t</span></samp>’ are reserved for additional type names. |
| </ul> |
| |
| <p>In addition, some individual header files reserve names beyond |
| those that they actually define. You only need to worry about these |
| restrictions if your program includes that particular header file. |
| |
| <ul> |
| <li>The header file <samp><span class="file">dirent.h</span></samp> reserves names prefixed with |
| ‘<samp><span class="samp">d_</span></samp>’. |
| <a name="index-dirent_002eh-28"></a> |
| <li>The header file <samp><span class="file">fcntl.h</span></samp> reserves names prefixed with |
| ‘<samp><span class="samp">l_</span></samp>’, ‘<samp><span class="samp">F_</span></samp>’, ‘<samp><span class="samp">O_</span></samp>’, and ‘<samp><span class="samp">S_</span></samp>’. |
| <a name="index-fcntl_002eh-29"></a> |
| <li>The header file <samp><span class="file">grp.h</span></samp> reserves names prefixed with ‘<samp><span class="samp">gr_</span></samp>’. |
| <a name="index-grp_002eh-30"></a> |
| <li>The header file <samp><span class="file">limits.h</span></samp> reserves names suffixed with ‘<samp><span class="samp">_MAX</span></samp>’. |
| <a name="index-limits_002eh-31"></a> |
| <li>The header file <samp><span class="file">pwd.h</span></samp> reserves names prefixed with ‘<samp><span class="samp">pw_</span></samp>’. |
| <a name="index-pwd_002eh-32"></a> |
| <li>The header file <samp><span class="file">signal.h</span></samp> reserves names prefixed with ‘<samp><span class="samp">sa_</span></samp>’ |
| and ‘<samp><span class="samp">SA_</span></samp>’. |
| <a name="index-signal_002eh-33"></a> |
| <li>The header file <samp><span class="file">sys/stat.h</span></samp> reserves names prefixed with ‘<samp><span class="samp">st_</span></samp>’ |
| and ‘<samp><span class="samp">S_</span></samp>’. |
| <a name="index-sys_002fstat_002eh-34"></a> |
| <li>The header file <samp><span class="file">sys/times.h</span></samp> reserves names prefixed with ‘<samp><span class="samp">tms_</span></samp>’. |
| <a name="index-sys_002ftimes_002eh-35"></a> |
| <li>The header file <samp><span class="file">termios.h</span></samp> reserves names prefixed with ‘<samp><span class="samp">c_</span></samp>’, |
| ‘<samp><span class="samp">V</span></samp>’, ‘<samp><span class="samp">I</span></samp>’, ‘<samp><span class="samp">O</span></samp>’, and ‘<samp><span class="samp">TC</span></samp>’; and names prefixed with |
| ‘<samp><span class="samp">B</span></samp>’ followed by a digit. |
| <a name="index-termios_002eh-36"></a></ul> |
| |
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