TIME-SYS.md

# 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.