HP OpenVMS Systems Documentation

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Run-Time Library Reference Manual for OpenVMS Systems

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Converts the argument, a wide character, to uppercase. If the argument is not a lowercase character, it is returned unchanged.


#include <wctype.h> (ISO C)

#include <wchar.h> (XPG4)

int towupper (wint_t wc);



An object of type wint_t representable as a valid wide character in the current locale, or the value of WEOF. For any other value, the behavior is undefined.


If the argument is a lowercase wide character, the corresponding uppercase wide character (as defined in the LC_CTYPE category of the locale) is returned, if it exists. If it does not exist, the function returns the input argument unchanged.

trunc (ALPHA, I64)

Truncates the argument to an integral value.


#include <math.h>

double trunc (double x);

float truncf (float x,);

long double truncl (long double x);



A floating-point number.

Return Value

n The truncated, integral value of the argument.


Changes file length to a specified length, in bytes.


#include <unistd.h>

int truncate (const char *path, off_t length);



The name of a file that is to be truncated. This argument must point to a pathname that names a regular file for which the calling process has write permission.


The new length of the file, in bytes. The off_t type of length is either a 64-bit or 32-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:



The truncate function changes the length of a file to the size, in bytes, specified by the length argument.

If the new length is less than the previous length, the function removes all data beyond length bytes from the specified file. All file data between the new End-of-File and the previous End-of-File is discarded.

For stream files, if the new length is greater than the previous length, new file data between the previous End-of-File and the new End-of-File is added, consisting of all zeros. (For record files, it is not possible to extend the file in this manner.)

Return Values

0 Indicates success.
- 1 An error occurred; errno is set to indicate the error.

ttyname, ttyname_r

Find the pathname of a terminal.


#include <unixio.h> (COMPATABILITY)

char *ttyname (void); (COMPATABILITY)

#include <unistd.h> (OPENVMS V7.3-2 AND HIGHER)

char *ttyname (int filedes); (OPENVMS V7.3-2 AND HIGHER)

int ttyname_r (int filedes, char name, size_t namesize); (OPENVMS V7.3-2 AND HIGHER), (ALPHA, I64)



An open file descriptor.


Pointer to a buffer in which the terminal name is stored.


The length of the buffer pointed to by the name argument.


The implementation of the ttyname function that takes no argument is provided only for backward compatibility. This legacy implementation returns a pointer to the null-terminated name of the terminal device associated with file descriptor 0, the default input device ( stdin ). A value of 0 is returned if SYS$INPUT is not a TTY device.

The ttyname_r function and the implementation of ttyname that takes a filedes argument are UNIX standard compliant and are available with only OpenVMS Version 7.3-2 and higher.

The standard compliant ttyname function returns a pointer to a string containing a null-terminated pathname of the terminal associated with file descriptor filedes. The return value might point to static data whose content is overwritten by each call. The ttyname interface need not be reentrant.

The ttyname_r function returns a pointer to store the null-terminated pathname of the terminal associated with the file descriptor filedes in the character array referenced by name. The array is namesize characters long and should have space for the name and the terminating null character. The maximum length of the terminal name is TTY_NAME_MAX.

If successful, ttyname returns a pointer to a string. Otherwise, a NULL pointer is returned and errno is set to indicate the error.

If successful, ttyname_r stores the terminal name as a null-terminated string in the buffer pointed to by name and returns 0. Otherwise, an error number is returned to indicate the error.

Return Values

x Upon successful completion, ttyname returns a pointer to a null-terminated string.
NULL Upon failure, ttyname returns a NULL pointer and sets errno to indicate the failure:
  • EBADF -- The fildes argument is not a valid file descriptor.
  • ENOTTY -- The fildes argument does not refer to a terminal device.
0 Upon successful completion, ttyname_r returns 0.
n Upon failure, ttyname_r sets errno to indicate the failure, and returns the same errno code:
  • EBADF -- The fildes argument is not a valid file descriptor.
  • ENOTTY -- The fildes argument does not refer to a TTY device.
  • ERANGE -- The value of namesize is smaller than the length of the string to be returned including the terminating null character.
0 For the legacy ttyname , indicates that SYS$INPUT is not a TTY device.


Sets and accesses time-zone conversion.


#include <time.h>

void tzset (void);

extern char *tzname[];

extern long int timezone;

extern int daylight;


The tzset function initializes time-conversion information used by the ctime , localtime , mktime , strftime , and wcsftime functions.

The tzset function sets the following external variables:

  • tzname is set as follows, where "std" is a 3-byte name for the standard time zone, and "dst" is a 3-byte name for the Daylight Savings Time zone:

    tzname[0] = "std"
    tzname[1] = "dst"
  • daylight is set to 0 if Daylight Savings Time should never be applied to the time zone. Otherwise, daylight is set to 1.
  • timezone is set to the difference between UTC and local standard time.

The environment variable TZ specifies how tzset initializes time conversion information:

  • If TZ is absent from the environment, the implementation-dependent time-zone information is used, as follows:
    The best available approximation to local wall-clock time is used, as defined by the SYS$LOCALTIME system logical, which points to a tzfile format file that describes default time-zone rules.
    This system logical is set during the installation of OpenVMS Version 7.0 or higher to define a time-zone file based off the root directory SYS$COMMON:[SYS$ZONEINFO.SYSTEM].1
  • If TZ appears in the environment but its value is a null string, Coordinated Universal Time (UTC) is used (without leap-second correction).
  • If TZ appears in the environment and its value is not a null string, the value has one of three formats, as described in Table REF-11.

Table REF-11 Time-Zone Initialization Rules
TZ Format Meaning
: UTC is used.
: pathname The characters following the colon specify the pathname of a tzfile format file from which to read the time-conversion information. A pathname beginning with a slash (/) represents an absolute pathname; otherwise, the pathname is relative to the system time-conversion information directory specified by SYS$TZDIR, which by default is SYS$COMMON:[SYS$ZONEINFO.SYSTEM].
stdoffset[ dst[ offset]
The value is first used as the pathname of a file (as described for the : pathname format) from which to read the time-conversion information.

If that file cannot be read, the value is then interpreted as a direct specification of the time-conversion information, as follows:

  std and dst---Three or more characters that are the designation for the time zone:
  • std---Standard time zone. Required.
  • dst---Daylight Savings Time zone. Optional. If dst is omitted, Daylight Savings Time does not apply.

Uppercase and lowercase letters are explicitly allowed. Any characters are allowed, except the following:

  • digits
  • leading colon (:)
  • comma (,)
  • minus ( - )
  • plus (+)
  • ASCII null character
  offset---The value added to the local time to arrive at UTC. The offset has the following format:

In this format:

  • hh (hours) is a one-or two-digit value of 0--24.
  • mm (minutes) is a value of 0--59. (optional)
  • ss (seconds) is a value of 0--59. (optional)
  The offset following std is required. If no offset follows dst, summer time is assumed, one hour ahead of standard time. You can use one or more digits; the value is always interpreted as a decimal number.

If the time zone is preceded by a minus sign ( - ), the time zone is East of Greenwich; otherwise, it is West, which can also be indicated by a preceding plus sign (+).

  rule---Indicates when to change to and return from summer time. The rule has the form:


  • start is the date when the change from standard time to summer time occurs.
  • end is the date for returning from summer time to standard time.
  If start and end are omitted, the default is the US Daylight Savings Time start and end dates. The format for start and end must be one of the following:
  • Jn---The Julian day n (1 < n < 365). Leap days are not counted. That is, in all years, including leap years, February 28 is day 59 and March 1 is day 60. You cannot explicitly refer to February 29.
  • n---The zero based Julian day (0 < n < 365). Leap days are counted, making it possible to refer to February 29.
  • Mm.n.d---The nth d day of month m, where:
    0 < n < 5
    0 < d < 6
    1 < m < 12

    When n is 5, it refers to the last d day of month m. Sunday is day 0.

  time---The time when, in current time, the change to or return from summer time occurs. The time argument has the same format as offset, except that you cannot use a leading minus ( - ) or plus (+) sign. If time is not specified, the default is 02:00:00.

If no rule is present in the TZ specification, the rules used are those specified by the tzfile format file defined by the SYS$POSIXRULES system logical in the system time-conversion information directory, with the standard and summer time offsets from UTC replaced by those specified by the offset values in TZ .

If TZ does not specify a tzfile format file and cannot be interpreted as a direct specification, UTC is used.


The UTC-based time functions, introduced in OpenVMS Version 7.0, had degraded performance compared with the non-UTC-based time functions.

OpenVMS Version 7.1 added a cache for time-zone files to improve performance. The size of the cache is determined by the logical name DECC$TZ_CACHE_SIZE. To accommodate most countries changing the time twice per year, the default cache size is large enough to hold two time-zone files.

See also ctime , localtime , mktime , strftime , and wcsftime .

Sample TZ Specification


This sample TZ specification describes the rule defined in 1987 for the Eastern time zone in the US:

  • EST (Eastern Standard Time) is the designation for standard time, which is 5 hours behind UTC.
  • EDT (Eastern Daylight Time) is the designation for summer time, which is 4 hours behind UTC. EDT starts on the first Sunday in April and ends on the last Sunday in October.

Because time was not specified in either case, the changes occur at the default time, which is 2:00 A.M. The start and end dates did not need to be specified, because they are the defaults.


1 The HP C RTL uses a public-domain, time-zone handling package that puts time-zone conversion rules in easily accessible and modifiable files. These files reside in the SYS$COMMON:[SYS$ZONEINFO.SYSTEM.SOURCES] directory. <tzfile.h> header file. The converted files are created with a root directory of SYS$COMMON:[SYS$ZONEINFO.SYSTEM], which is pointed to by the SYS$TZDIR system logical. This format is readable by the C library functions that handle time-zone information. For example, in the eastern United Stated, SYS$LOCALTIME is defined to be SYS$COMMON:[SYS$ZONEINFO.SYSTEM.US]EASTERN.


Sets or changes the timeout of interval timers.


#include <unistd.h>

useconds_t ualarm (useconds_t mseconds, useconds_t interval);



Specifies a number of real-time microseconds.


Specifies the interval for repeating the timer.


The ualarm function causes the SIGALRM signal to be generated for the calling process after the number of real-time microseconds specified by useconds has elapsed. When the interval argument is nonzero, repeated timeout notification occurs with a period in microseconds specified by interval. If the notification signal SIGALRM is not caught or is ignored, the calling process is terminated.

If you call a combination of ualarm and setitimer functions, and the AST status is disabled, the return value is invalid.

If you call a combination of ualarm and setitimer functions, and the AST status is enabled, the return value is valid.

This is because you cannot invoke an AST handler to clear the previous value of the timer when ASTs are disabled or invoked from a handler that was invoked at AST level.


Interactions between ualarm and either alarm , or sleep are unspecified.

See also setitimer .

Return Values

n The number of microseconds remaining from the previous ualarm or setitimer call.
0 No timeouts are pending or ualarm not previously called.
- 1 Indicates an error.


Creates a file protection mask that is used when a new file is created, and returns the previous mask value.


#include <stat.h>

mode_t umask (mode_t mode_complement);



Shows which bits to turn off when a new file is created. See the description of chmod to determine what the bits represent.


Initially, the file protection mask is set from the current process's default file protection. This is done when the C main program starts up or when DECC$CRTL_INIT (or VAXC$CRTL_INIT ) is called. You can change this for all files created by your program by calling umask or you can use chmod to change the file protection on individual files. The file protection of a file created by open or creat is the bitwise AND of the open and creat mode argument with the complement of the value passed to umask on the previous call.


The way to create files with OpenVMS RMS default protections using the UNIX system-call functions umask , mkdir , creat , and open is to call mkdir , creat , and open with a file-protection mode argument of 0777 in a program that never specifically calls umask . These default protections include correctly establishing protections based on ACLs, previous versions of files, and so on.

In programs that do vfork / exec calls, the new process image inherits whether umask has ever been called or not from the calling process image. The umask setting and whether the umask function has ever been called are both inherited attributes.

Return Value

x The old mask value.

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