# TIME-SYS ## **Overview** Provides time-related structures and functions. **Since:** 1.0 **Version:** 1.0 ## **Summary** ## Files

File Name

Description

time.h

Provides structures and functions related to the system time.

## Data Structures

Data Structure Name

Description

timeval

Describes a period of time, accurate to microseconds.

timespec

Describes a period of time, accurate to nanoseconds.

itimerval

Describes a timer.

timezone

Describes a time zone.

## Macros

Macro Name and Value

Description

ITIMER_REAL    0

Defines the timer that runs in real time.

## Functions

Function Name

Description

gettimeofday (struct timeval *__restrict value, void *__restrict ovalue)

int 

Obtains the system time and time zone.

getitimer (int w, struct itimerval *old)

int 

Obtains the value of an intermittent timer.

setitimer (int w, const struct itimerval *__restrict value, struct itimerval *__restrict ovalue)

int 

Sets the value for a timer.

settimeofday (const struct timeval *tv, const struct timezone *tz)

int 

Sets the system time and time zone.

## **Details** ## **Function Documentation** ## getitimer\(\) ``` int getitimer (int w, struct [itimerval](itimerval.md) * old ) ``` **Description:** Obtains the value of an intermittent timer. **Parameters:**

Name

Description
w Indicates the timer type. Only ITIMER_REAL is supported.
old Indicates the pointer to the timer value.
**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno

Description

EINVAL

Incorrect input or timer type.

## gettimeofday\(\) ``` int gettimeofday (struct [timeval](timeval.md) *__restrict value, void *__restrict ovalue ) ``` **Description:** Obtains the system time and time zone. **Parameters:**

Name

Description
value Indicates the pointer to the timeval structure that contains the time.
ovalue This parameter is used for compatibility only.
**Attention:** Currently, there is no time zone structure. The return value of **ovalue** is empty. **Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno

Description

EINVAL

Incorrect input.

## setitimer\(\) ``` int setitimer (int w, const struct [itimerval](itimerval.md) *__restrict value, struct [itimerval](itimerval.md) *__restrict ovalue ) ``` **Description:** Sets the value for a timer. **Parameters:**

Name

Description
w Indicates the timer type. Currently, only ITIMER_REAL is supported.
value Indicates the pointer to the timer value to set.
ovalue Indicates the pointer to the original timer value before the current setting, which can be NULL.
**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno

Description

EINVAL

Incorrect input or timer type.

## settimeofday\(\) ``` int settimeofday (const struct [timeval](timeval.md) * tv, const struct [timezone](timezone.md) * tz ) ``` **Description:** Sets the system time and time zone. **Parameters:**

Name

Description
tv Indicates the pointer to the time to set.
tz Indicates the pointer to the time zone to set. This parameter is not used yet.
**Attention:** **tz** is invalid. The time is set internally using **clock\_settime**. **Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno

Description

EINVAL

Incorrect input.