HP OpenVMS Systems Documentation

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Run-Time Library Reference Manual for OpenVMS Systems

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An alphabetic listing and description of the C RTL feature logical names follows. Unless otherwise stated, the feature logicals are enabled with ENABLE and disabled with DISABLE.


The DECC$ACL_ACCESS_CHECK feature logical controls the behavior of the access function.

With DECC$ACL_ACCESS_CHECK enabled, the access function checks both UIC protection and OpenVMS Access Control Lists (ACLs).

With DECC$ACL_ACCESS_CHECK disabled, the access function checks only UIC protection.


The DECC$ALLOW_REMOVE_OPEN_FILES feature logical controls the behavior of the remove function on open files. Ordinarily, the operation fails. However, POSIX conformance dictates that the operation succeed.

With DECC$ALLOW_REMOVE_OPEN_FILES enabled, this POSIX conformant behavior is achieved.


With DECC$ALLOW_UNPRIVILEGED_NICE enabled, the nice function exhibits its legacy behavior of not checking the privilege of the calling process (that is, any user may lower the nice value to increase process priorities). Also, when the caller sets a priority above MAX_PRIORITY, the nice value is set to the base priority.

With DECC$ALLOW_UNPRIVILEGED_NICE disabled, the nice function conforms to the X/Open standard of checking the privilege of the calling process (only users with ALTPRI privilege can lower the nice value to increase process priorities), and when the caller sets a priority above MAX_PRIORITY, the nice value is set to MAX_PRIORITY.


With DECC$ARGV_PARSE_STYLE enabled, case is preserved in command-line arguments when the process has been set up for extended DCL parsing using SET PROCESS/PARSE_STYLE=EXTENDED.

DECC$ARGV_PARSE_STYLE must be defined externally as a logical name or set in a function called using the LIB$INITIALIZE mechanism because it is evaluated before function main is called.


DECC$DEFAULT_LRL specifies the default value for the RMS attribute for the longest record length. The default value 32767 is the largest record size supported by RMS.

Default: 32767

Maximum: 32767


With DECC$DEFAULT_UDF_RECORD enabled, file access mode defaults to RECORD instead of STREAM mode for all files except STREAMLF.


With DECC$DETACHED_CHILD_PROCESS enabled, child processes created using vfork and exec are created as detached processes instead of subprocesses.

This feature has only limited support. In some cases the console cannot be shared between the parent process and the detached process, which can cause exec to fail.


With DECC$DISABLE_POSIX_ROOT enabled, support for the POSIX root directory defined by SYS$POSIX_ROOT is disabled.

With DECC$DISABLE_POSIX_ROOT disabled, the SYS$POSIX_ROOT logical name is interpreted as the equivalent of the file path "/". If a UNIX path starting with a slash (/) is given and the value after the leading slash cannot be translated as a logical name, SYS$POSIX_ROOT is used as the parent directory for the specified UNIX file path.

The C RTL supports a UNIX style root that behaves like a real directory. This allows such actions as:

% cd /
% mkdir /dirname
% tar -xvf tarfile.tar /dirname
% ls /

Previously, the C RTL did not recognize "/" as a directory name. The normal processing for a file path starting with "/" was to interpret the first element as a logical name or device name. If this failed, there was special processing for the name /dev/null and names starting with /bin and /tmp :

/dev/null       NLA0:
/bin            SYS$SYSTEM:
/tmp            SYS$SCRATCH:

These behaviors are retained for compatibility purposes. In addition, support has been added to the C RTL for the logical name SYS$POSIX_ROOT as an equivalent to "/".

To enable this feature for use by the C RTL, define SYS$POSIX_ROOT as a concealed logical name. For example:


To disable this feature:


Enabling SYS$POSIX_ROOT results in the following behavior:

  • If the existing translation of a UNIX path starting with "/" fails and SYS$POSIX_ROOT is defined, the name is interpreted as if it starts with /sys$posix_root .
  • When converting from an OpenVMS to a UNIX style file name, and the OpenVMS name starts with "SYS$POSIX_ROOT:", then the "SYS$POSIX_ROOT:" is removed. For example, SYS$POSIX_ROOT:[dirname] becomes /dirname . If the resulting name could be interpreted as a logical name or one of the special cases previously listed, the result is /./dirname instead of /dirname .


With DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION enabled, the conversion routine decc$to_vms will only treat the first element of a UNIX style name as a logical name if there is a leading slash (/).


With DECC$EFS_CASE_PRESERVE enabled, case is preserved for file names on ODS-5 disks.

With DECC$EFS_CASE_PRESERVE disabled, UNIX style file names are always reported in lowercase.

However, note that enabling DECC$EFS_CASE_SPECIAL overrides the setting for DECC$EFS_CASE_PRESERVE.


With DECC$EFS_CASE_SPECIAL enabled, case is preserved only for file names containing lowercase. If an element of a file name contains all uppercase letters, it is reported in all lowercase in UNIX style.

When enabled, DECC$EFS_CASE_SPECIAL overrides the value of DECC$EFS_CASE_PRESERVE.


With DECC$EFS_CHARSET enabled, UNIX names can contain ODS-5 extended characters. Support includes multiple dots and all ASCII characters in the range 0 to 255, except the following:

/         *
"         ?

Unless DECC$FILENAME_UNIX_ONLY is enabled, some characters can be interpreted as OpenVMS characters depending on context. They are:

:         ^
[         ;

DECC$EFS_CHARSET might be necessary for existing applications that make assumptions about file names based on the presence of certain characters, because the following nonstandard and undocumented C RTL extensions do not work when EFS extended character-set support is enabled:

  • $HOME is interpreted as the user's login directory
    With DECC$EFS_CHARSET enabled, $HOME is treated literally and may be in an OpenVMS or UNIX style file name.
  • ~name is interpreted as the login directory for user name
    With DECC$EFS_CHARSET enabled, ~name is treated literally and can be in an OpenVMS or UNIX style file name.
  • Wild card regular expressions in the form [a-z]
    With DECC$EFS_CHARSET enabled, square brackets are acceptable in OpenVMS and UNIX style file names. For instance, in a function such as open , abc[a-z]ef.txt is interpreted as a UNIX style name equivalent to the OpenVMS style name abc^[a-z^]ef.txt , and [a-z]bc is interpreted as an OpenVMS style name equivalent to the UNIX style name /sys$disk/a-z/bc .

With DECC$EFS_CHARSET enabled, the following encoding for EFS extended characters is supported when converting from an OpenVMS style file name to a UNIX style file name:

  • All ODS-2 compatible names
  • All encoding for 8-bit characters, either as single byte or using two-digit hexadecimal form ^ab . In a UNIX path these are always represented as a single byte.
  • Encoding for DEL (^7F)
  • The following characters when preceded by a caret:

    space ! , _ & ' ( ) + @ { } ; # [ ] % ^ = $ - ~ .
  • The following characters when not preceded by a caret:

    $  -  ~  .
  • The implementation supports the conversion from OpenVMS to UNIX needed for functions readdir , ftw , getname , fgetname , getcwd , and others.


With DECC$EFS_FILE_TIMESTAMPS enabled, stat and fstat report new ODS-5 access time ( st_atime ), attribute revision time ( st_ctime ) and modification time ( st_mtime ) for files on ODS-5 volumes that have the extended file times enabled using SET VOLUME/VOLUME=ACCESS_DATES.

If DECC$EFS_FILE_TIMESTAMPS is disabled, or the volume is not ODS-5, or the volume does not have support for these additional times enabled, st_ctime continues to be the file creation time and st_atime the same as the st_mtime .

The utime and utimes functions support these ODS-5 times in the same way as stat .


With support for extended characters in file names for ODS-5, a name such as NAME.EXT can be interpreted as NAME.EXT.DIR. Determining if directory [.name^.ext] exists adds overhead to UNIX name translation when support for extended character support in UNIX file names is enabled.

Enabling the DECC$EFS_NO_DOTS_IN_DIRNAME feature logical suppresses the interpretation of a file name containing dots as a directory name. With this logical enabled, NAME.EXT is assumed to be a file name; no check is made for directory [.name^.ext].


The C RTL supplements the list of environment variables in the environ table with all logical names and DCL symbols available to the process.

By default, whenever getenv is called for a name not in the environ table, an attempt is made to resolve this as a logical name and, if this fails, as a DCL symbol.

With DECC$ENABLE_GETENV_CACHE enabled, once a logical name or DCL name has been successfully translated, its value is stored in a cache. When the same name is requested in a future call to getenv , the value is returned from the cache instead of reevaluating the logical name or DCL symbol.


Use the DECC$ENABLE_TO_VMS_LOGNAME_CACHE to improve the performance of UNIX name translation. The value is the life of each cache entry in seconds. The equivalence string ENABLE is evaluated as 1 second.

Define DECC$ENABLE_TO_VMS_LOGNAME_CACHE to 1 to enable the cache with a 1-second life for each entry.

Define DECC$ENABLE_TO_VMS_LOGNAME_CACHE to 2 to enable the cache with a 2-second life for each entry.

Define DECC$ENABLE_TO_VMS_LOGNAME_CACHE to - 1 to enable the cache without a cache entry expiration.


The DECC$EXEC_FILEATTR_INHERITANCE feature logical affects child processes that are C programs.

For versions of OpenVMS before Version 7.3-2, DECC$EXEC_FILEATTR_INHERITANCE is either enabled or disabled:

  • With DECC$EXEC_FILEATTR_INHERITANCE enabled, the current file pointer and the file open mode is passed to the child process in exec calls.
  • With this logical name disabled, the child process does not inherit append mode or the file position.

For OpenVMS Version 7.3-2 and higher, DECC$EXEC_FILEATTR_INHERITANCE can be defined to 1 or 2, or be disabled:

  • With DECC$EXEC_FILEATTR_INHERITANCE defined to 1, a child process inherits file positioning for all file access modes except append.
  • With DECC$EXEC_FILEATTR_INHERITANCE defined to 2, a child process inherits file positioning for all file access modes including append.
  • With DECC$EXEC_FILEATTR_INHERITANCE disabled, a child process does not inherit the file position for any access modes.


With DECC$FILENAME_UNIX_ONLY enabled, file names are never interpreted as OpenVMS style names. This prevents any interpretation of the following as OpenVMS special characters:

:   [   ^


With DECC$FILENAME_UNIX_NO_VERSION enabled, OpenVMS version numbers are not supported in UNIX style file names.

With DECC$FILENAME_UNIX_NO_VERSION disabled, in UNIX style names, version numbers are reported preceded by a period (.).


With DECC$FILENAME_UNIX_REPORT enabled, all file names are reported in UNIX style unless the caller specifically selects OpenVMS style. This applies to getpwnam , getpwuid , argv[0] , getname , fgetname , and tempnam .

With DECC$FILENAME_UNIX_REPORT disabled, unless specified in the function call, file names are reported in OpenVMS style.


With DECC$FILE_PERMISSION_UNIX enabled, the file permissions for new files and directories are set according to the file creation mode and umask . This includes mode 0777. When an earlier version of the file exists, the file permissions for the new file are inherited from the earlier version. This mode sets DELETE permission for a new directory when WRITE permission is enabled.

With DECC$FILE_PERMISSION_UNIX disabled, modes 0 and 0777 indicate using RMS default protection or protection from the previous version of the file. Permissions for new directories also follow OpenVMS rules, including disabling DELETE permissions.


With DECC$FILE_SHARING enabled, all files are opened with full sharing enabled (FAB$M_DEL | FAB$M_GET | FAB$M_PUT | FAB$M_UPD). This is set as a logical OR with any sharing mode specified by the caller.


With DECC$FIXED_LENGTH_SEEK_TO_EOF enabled, lseek , fseeko , and fseek with the direction paremeter set to SEEK_END will position relative to the last byte in the file for files with fixed-length records.

With DECC$FIXED_LENGTH_SEEK_TO_EOF disabled, lseek , fseek , and fseeko when called with SEEK_EOF on files with fixed-length records, will position relative to the end of the last record in the file.


Enabling DECC$GLOB_UNIX_STYLE selects the UNIX mode of the glob function, which uses UNIX style filenames and wildcards instead of OpenVMS style filenames and wildcards.


DECC$LOCALE_CACHE_SIZE defines how much memory, in bytes, to allocate for caching locale data. The default value is 0, which disables the locale cache.

Default: 0

Maximum: 2147483647


By default, an open on a local mailbox that is not a pipe treats mailbox records as having a record attribute of FAB$M_CR.

With DECC$MAILBOX_CTX_STM enabled, the record attribute FAB$M_CR is not set.


When the decc$to_vms function evaluates a UNIX style path string, if it determines the first element to be a logical name, then:
  • For rooted logicals or devices, it appends ":[000000]" to the logical name.
    For example, if log1 is a rooted logical ($DEFINE LOG1 [DIR_NAME.]) then /log1/filename.ext translates to LOG1:[000000]FILENAME.EXT.
  • For nonrooted logicals, it appends just a colon (:) to the logical name.
    For example, if log2 is a nonrooted logical ($ DEFINE LOG2 [DIR_NAME]), then /log2/filename.ext translates to LOG2:FILENAME.EXT.
  • If the first element is a search-list logical, the translation proceeds by evaluating the first element in the search list, and translating the path as previously described.

The preceding three cases lead to predictable, expected results.

In the case where the first element is a search list that consists of a mixture of rooted and nonrooted logicals, translating paths as described previously can lead to different behavior from that of older versions of OpenVMS (before OpenVMS Version 7.3-1):

  • Before OpenVMS Version 7.3-1, regardless of the contents of the logical, the decc$to_vms function appended only a colon (:). For search lists that consisted of a mixture of rooted and nonrooted logicals, this resulted in certain expected behaviors.
  • For OpenVMS Version 7.3-1 and later, if the first element of the mixed search list is a rooted logical, then decc$to_vms appends ":[000000]" to the logical name, resulting in different behavior from that of OpenVMS releases prior to Version 7.3-1.

DECC$NO_ROOTED_SEARCH_LISTS controls how the decc$to_vms function resolves search-list logicals and provides a means to restore the OpenVMS behavior prior to Version 7.3-1.


  • If a logical is detected in a file specification, and it is a search list, then a colon (:) is appended when forming the OpenVMS file specification.
  • If it is not a search list, the behavior is the same as with DECC$NO_ROOTED_SEARCH_LISTS disabled.

Enabling this feature logical provides the pre-Version 7.3-1 behavior for search list logicals.


  • If a logical is detected in a file specification, and it is a rooted logical (or a search list whose first element is a rooted logical), then ":[000000]" is appended when forming the OpenVMS file specification.
  • If it is a nonrooted logical (or a search list whose first element is a nonrooted logical), then just a colon (:) is appended.

Disabling this feature logical provides the behavior for OpenVMS Version 7.3-1 and later.


The system default buffer size of 512 bytes for pipe write operations can limit performance and generate extra line feeds when handling messages longer than 512 bytes.

DECC$PIPE_BUFFER_SIZE allows a larger buffer size to be used for pipe functions such as pipe and popen . A value of 512 to 65535 bytes can be specified.

If DECC$PIPE_BUFFER_SIZE is not specified, the default buffer size 512 is used.

Default: 512

Minimum: 512

Maximum: 65535


OpenVMS Version 7.3-2 adds an optional fourth argument of type int to the pipe function to specify the buffer quota of the pipe's mailbox. In previous OpenVMS versions, the buffer quota was equal to the buffer size.

DECC$PIPE_BUFFER_QUOTA lets you specify a buffer quota to use for the pipe function if the optional fourth argument of that function is omitted.

If the optional pipe fourth argument is omitted and DECC$PIPE_BUFFER_QUOTA is not defined, then the buffer quota defaults to the buffer size, as before.

Default: 512

Minimum: 512

Maximum: 2147483647


With DECC$POPEN_NO_CRLF_REC_ATTR disabled, a pipe opened with the popen function has its record attributes set to CR/LF carriage control (fab$b_rat |= FAB$M_CR). This is the default behavior.

With DECC$POPEN_NO_CRLF_REC_ATTR enabled, CR/LF carriage control is prevented from being added to the pipe records. This is compatible with UNIX behavior, but be aware that enabling this feature might result in undesired behavior from other functions, such as gets , that rely on the carriage-return character.


With DECC$POSIX_SEEK_STREAM_FILE enabled, positioning beyond end-of-file on STREAM files does not write to the file until the next write. If the write is beyond the current end-of-file, this positions beyond the old end-of-file, and the start position for the write is filled with zeros.

With DECC$POSIX_SEEK_STREAM_FILE disabled, positioning beyond end-of-file will immediately write zeros to the file from the current end-of-file to the new position.


With DECC$POSIX_STYLE_UID enabled, 32-bit UIDs and GIDs are interpreted as POSIX style identifiers.

With this logical name disabled, UIDs and GIDs are derived from the process UIC.

This feature is only available on OpenVMS systems providing POSIX style UID and GID support.


With DECC$READDIR_DROPDOTNOTYPE enabled, readdir when reporting files in UNIX style only reports the trailing period (.) for files with no file type when the file name contains a period.

With this logical name disabled, all files without a file type are reported with a trailing period.


The default behavior when reporting files in UNIX style from readdir is to report directories without a file type.

With DECC$READDIR_KEEPDOTDIR enabled, directories are reported in UNIX style with a file type of ".DIR".


DECC$RENAME_NO_INHERIT provides more UNIX compliant behavior in the rename function. With DECC$RENAME_NO_INHERIT enabled, the following behaviors are enforced:
  • If the old argument points to the pathname of a file that is not a directory, the new argument will not point to the pathname of a directory.
  • The new argument cannot point to a directory that exists.
  • If the old argument points to the pathname of a directory, the new argument will not point to the pathname of a file that is not a directory.
  • The new name for the file does not inherit anything from the old name. The new name must be specified completely. For example:
    Renaming "A.A" to "B" yields "B"

With this logical name disabled, you get the expected OpenVMS behavior. For example:

Renaming "A.A" to "B" yields "B.A"


Enabling DECC$RENAME_ALLOW_DIR restores the prior OpenVMS behavior of the rename function by allowing conversion to a directory specification when the second argument is an ambiguous file specification passed as a logical name. The ambiguity is whether the logical name is a UNIX or OpenVMS file specification. Consider the following example with DECC$RENAME_ALLOW_DIR enabled:

rename("file.ext", "logical_name")  /* where logical_name = dev:[dir.subdir] */
                                    /* and :[dir.subdir] exists              */

This results in:


This example renames a file from one directory into another directory, which is the same behavior as in legacy versions of OpenVMS (versions before 7.3-1). Also in this example, if dev:[dir.subdir] does not exist, rename returns an error.

Disabling DECC$RENAME_ALLOW_DIR provides a more UNIX compliant conversion of the "logical_name" argument of rename . Consider the following example with DECC$RENAME_ALLOW_DIR disabled:

rename("file.ext", "logical_name")   /* where logical_name = dev:[dir.subdir] */

This results in:


This example renames the file using the subdir part of the "logical_name" argument as the new file name because on UNIX systems, renaming a file to a directory is not allowed. So rename internally converts the "logical_name" to a file name, and dev:[dir]subdir is the most reasonable conversion it can perform.

This new feature switch has a side effect of causing rename to a directory to take precedence over rename to a file. Consider this example:

rename ( "file1.ext", "dir2" )      /* dir2 is not a logical */

With DECC$RENAME_ALLOW_DIR disabled, this example results in dir2.ext , regardless of whether or not subdirectory [.dir2] exists.

With DECC$RENAME_ALLOW_DIR enabled, this example results in dir2.ext only if subdirectory [.dir2] does not exist. If subdirectory [.dir2] does exist, the result is [.dir2]file1.ext .


If DECC$RENAME_NO_INHERIT is enabled, UNIX compliant behavior is expected, so DECC$RENAME_ALLOW_DIR is ignored, and renaming a file to a directory is not allowed.


With DECC$SELECT_IGNORES_INVALID_FD enabled, select fails with errno set to EBADF when an invalid file descriptor is specified in one of the descriptor sets.

With DECC$SELECT_IGNORES_INVALID_FD disabled, select ignores invalid file descriptors.


With DECC$STDIO_CTX_EOL enabled, writing to stdout and stderr for stream access is deferred until a terminator is seen or the buffer is full.

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