(libc.info.gz) Reserved Names

Info Catalog

(libc.info.gz) Macro Definitions

(libc.info.gz) Using the Library

(libc.info.gz) Feature Test Macros

 
 1.3.3 Reserved Names
 --------------------
 
 The names of all library types, macros, variables and functions that
 come from the ISO C standard are reserved unconditionally; your program
 *may not* 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:
 
    * Other people reading your code could get very confused if you were
      using a function named 'exit' to do something completely different
      from what the standard 'exit' function does, for example.
      Preventing this situation helps to make your programs easier to
      understand and contributes to modularity and maintainability.
 
    * 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.
 
    * 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 ( Variadic
      Functions) and non-local exits ( Non-Local Exits),
      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.
 
    In addition to the names documented in this manual, reserved names
 include all external identifiers (global functions and variables) that
 begin with an underscore ('_') 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.
 
    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.
 
    * Names beginning with a capital 'E' followed a digit or uppercase
      letter may be used for additional error code names.   Error
      Reporting.
 
    * Names that begin with either 'is' or 'to' followed by a lowercase
      letter may be used for additional character testing and conversion
      functions.   Character Handling.
 
    * Names that begin with 'LC_' followed by an uppercase letter may be
      used for additional macros specifying locale attributes.  
      Locales.
 
    * Names of all existing mathematics functions ( Mathematics)
      suffixed with 'f' or 'l' are reserved for corresponding functions
      that operate on 'float' and 'long double' arguments, respectively.
 
    * Names that begin with 'SIG' followed by an uppercase letter are
      reserved for additional signal names.   Standard Signals.
 
    * Names that begin with 'SIG_' followed by an uppercase letter are
      reserved for additional signal actions.   Basic Signal
      Handling.
 
    * Names beginning with 'str', 'mem', or 'wcs' followed by a lowercase
      letter are reserved for additional string and array functions.
       String and Array Utilities.
 
    * Names that end with '_t' are reserved for additional type names.
 
    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.
 
    * The header file 'dirent.h' reserves names prefixed with 'd_'.
 
    * The header file 'fcntl.h' reserves names prefixed with 'l_', 'F_',
      'O_', and 'S_'.
 
    * The header file 'grp.h' reserves names prefixed with 'gr_'.
 
    * The header file 'limits.h' reserves names suffixed with '_MAX'.
 
    * The header file 'pwd.h' reserves names prefixed with 'pw_'.
 
    * The header file 'signal.h' reserves names prefixed with 'sa_' and
      'SA_'.
 
    * The header file 'sys/stat.h' reserves names prefixed with 'st_' and
      'S_'.
 
    * The header file 'sys/times.h' reserves names prefixed with 'tms_'.
 
    * The header file 'termios.h' reserves names prefixed with 'c_', 'V',
      'I', 'O', and 'TC'; and names prefixed with 'B' followed by a
      digit.
 

Info Catalog

(libc.info.gz) Macro Definitions

(libc.info.gz) Using the Library

(libc.info.gz) Feature Test Macros