The C RTL provides an extensive list of feature switches that
    can be set using DECC$ logical names. These switches affect the
    behavior of a C application at run time.

    The feature switches introduce new behaviors and also preserve
    old behaviors that have been deprecated.

    You enable most features by setting a logical name to ENABLE and
    disable a feature by setting the logical name to DISABLE:

    $ DEFINE DECC$feature ENABLE

    $ DEFINE DECC$feature DISABLE

    Some feature logical names can be set to a numeric value. For
    example:

    $ DEFINE DECC$PIPE_BUFFER_SIZE 32768

                                  NOTES

       o  Do not set C RTL feature logical names for the system.
          Set them only for the applications that need them,
          because other applications including OpenVMS components
          depend on the default behavior of these logical names.

       o  Older feature logicals from earlier releases of the
          C Run-Time Library were documented as supplying "any
          equivalence string" to enable a feature. While this was
          true at one time, we now strongly recommend that you use
          ENABLE for setting these feature logicals and DISABLE for
          disabling them. Failure to do so may produce unexpected
          results.

          The reason for this is twofold:

          -  In previous versions of the C RTL, any equivalence
             string, even DISABLE, may have enabled a feature
             logical.

          -  In subsequent and current versions of the C RTL, the
             following equivalence strings will disable a feature
             logical. Do not use them to enable a feature logical.

                DISABLE
                0 (zero)
                F
                FALSE
                N
                NO

             Any other string not on this list will enable a
             feature logical. The unintentionally misspelled string
             "DSABLE", for example, will enable a feature logical.

    The C RTL also provides several functions to manage feature
    logicals within your applications:

    decc$feature_get
    decc$feature_get_value
    decc$feature_get_index
    decc$feature_get_name
    decc$feature_set
    decc$feature_set_value
    decc$feature_show
    decc$feature_show_all

    See the reference section for more information on these
    functions.

    The C RTL feature logical names are listed below, grouped by the
    type of features they control:

       Feature Logical Name               Default
       ------- ------- ----               -------

       Performance Optimizations:

          DECC$ENABLE_GETENV_CACHE        DISABLE
          DECC$LOCALE_CACHE_SIZE          0
          DECC$TZ_CACHE_SIZE              2

       Legacy Behaviors:

          DECC$ALLOW_UNPRIVILEGED_NICE    DISABLE
          DECC$NO_ROOTED_SEARCH_LISTS     DISABLE
          DECC$PRINTF_USES_VAX_ROUND      DISABLE
          DECC$THREAD_DATA_AST_SAFE       DISABLE
          DECC$V62_RECORD_GENERATION      DISABLE
          DECC$WRITE_SHORT_RECORDS        DISABLE
          DECC$XPG4_STRPTIME              DISABLE

       File Attributes:

          DECC$DEFAULT_LRL                32767
          DECC$DEFAULT_UDF_RECORD         DISABLE
          DECC$FIXED_LENGTH_SEEK_TO_EOF   DISABLE
          DECC$ACL_ACCESS_CHECK           DISABLE

       Mailboxes:

          DECC$MAILBOX_CTX_STM            DISABLE

       Changes for UNIX Conformance:

          DECC$SELECT_IGNORES_INVALID_FD  DISABLE
          DECC$STRTOL_ERANGE              DISABLE
          DECC$VALIDATE_SIGNAL_IN_KILL    DISABLE

       General UNIX Enhancements:

          DECC$UNIX_LEVEL                 DISABLE
          DECC$ARGV_PARSE_STYLE           DISABLE
          DECC$PIPE_BUFFER_SIZE           512
          DECC$PIPE_BUFFER_QUOTA          512
          DECC$STREAM_PIPE                DISABLE
          DECC$POPEN_NO_CRLF_REC_ATTR     DISABLE
          DECC$STDIO_CTX_EOL              DISABLE
          DECC$USE_RAB64                  DISABLE
          DECC$GLOB_UNIX_STYLE            DISABLE

       Enhancements for UNIX Style Filenames:

          DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION  DISABLE
          DECC$EFS_CHARSET                  DISABLE
          DECC$ENABLE_TO_VMS_LOGNAME_CACHE  ENABLE
          DECC$FILENAME_ENCODING_UTF8       DISABLE
          DECC$FILENAME_UNIX_NO_VERSION     DISABLE
          DECC$FILENAME_UNIX_REPORT         DISABLE
          DECC$READDIR_DROPDOTNOTYPE        DISABLE
          DECC$RENAME_NO_INHERIT            DISABLE
          DECC$RENAME_ALLOW_DIR             DISABLE

       Enhancements for UNIX Style File Attributes:

          DECC$EFS_FILE_TIMESTAMPS        DISABLE
          DECC$EXEC_FILEATTR_INHERITANCE  DISABLE
          DECC$FILE_OWNER_UNIX            DISABLE
          DECC$FILE_PERMISSION_UNIX       DISABLE
          DECC$FILE_SHARING               DISABLE

       UNIX Compliance Mode:

          DECC$DETACHED_CHILD_PROCESS     DISABLE
          DECC$FILENAME_UNIX_ONLY         DISABLE
          DECC$POSIX_STYLE_UID            DISABLE
          DECC$USE_JPI$_CREATOR           DISABLE

       New Behaviors for POSIX Conformance:

          DECC$ALLOW_REMOVE_OPEN_FILES    DISABLE
          DECC$POSIX_SEEK_STREAM_FILE     DISABLE
          DECC$UMASK                      RMS default

       Filename Handling:

          DECC$POSIX_COMPLIANT_PATHNAMES  DISABLE

          DECC$DISABLE_POSIX_ROOT         ENABLE
          DECC$EFS_CASE_PRESERVE          DISABLE
          DECC$EFS_CASE_SPECIAL           DISABLE
          DECC$EFS_NO_DOTS_IN_DIRNAME     DISABLE
          DECC$READDIR_KEEPDOTDIR         DISABLE
          DECC$UNIX_PATH_BEFORE_LOGNAME   DISABLE