In this chapter the existing functions will be studied in PHP for the employment of dates. This type of functions exists in most of computer languages and it are faced to his securing and representation in different formats.

The time in any computer language usually takes with regard to the beginning of "it was UNIX" that is January 1, 1970 to 0:00:00 AM. The simplest function that is based on this time mark is the function steal () whose returned value is the entire number that represents the mark of time corresponding to the moment in which the function was executed with regard to the age unix.

In some applications it is necessary to possess a more detailed time mark and for it we use microswindle () that returns a chain of characters with the seconds and microseconds.

In case we will want to take as a value of reference the hour of the computer from which it is executed we would use the function gettimeofday () in which we would pass for an internal parameter, sec (to know the second ones), usec (microseconds), minuteswest (nº seconds to the west of greenwich) and dstime (type of correction in daylight saving times and I hibernate).

These functions quoted previously are little used since the existence of other more finished functions, like for example the function getdate () that obtains an associative counterfoil with the information of the date and hour of the system. The elements of the above mentioned counterfoil are:

If we do not spend any parameter to him to the function then the current hour of the system is considered and if there is received like parameter an entire number of that time it turns it to the corresponding date.

Another function to obtain the hour is the function localtime (marca_tiempo, tipo_matriz); whose values we happen to comment next:

Formats of dates

The functions seen previously were allowing us to turn the entire value of the date into a value more easily understandable, although to be able to gain access to the above mentioned information it is necessary to happen for the previous step of obtaining a counterfoil. To avoid this intermediate step, PHP puts at your disposal the funcióndate (format, marca_tiempo);

This function returns us a chain of characters that corresponds with a date to which a certain format has been applied. To define the format of the date he gets ready of the following options:

The function strftime () represents another possibility to apply formats to a date. This function uses the local conventions of the machine from which the script is executed to return a chain with the format defined in the chosen language. His format remains defined by the following values:

Establishing hours and dates

As soon as there was known the way of obtaining the current date, it is necessary to have a way of being able to fix a certain hour to establish for example the expiry date of a cookie, that is to say, the way of obtaining a mark of time corresponding to a certain hour.

For it PHP has two functions that are mktime () and gmmktime () whose functioning we will explain next:

The function mktime (hour, minute, second, month, day, year, [adjustment-> 0 daylight saving time and 1 winter]); he returns us an entire value that represents the time mark UNIX of a certain date. Each of the mentioned values can be omitted any time from the omitted value values are not represented any more to his right.

The function gmmktime () works of the same form what thinks that the parameters represent one hour GMT.

The function setlocale (category, country); to we allow to establish the language in those who will appear the date, hour, etc. The possible categories are:

Ratification of dates

There exist numerous occasions in which the creation of a system is necessary to verify if the date introduced by the user is cost or not. For it PHP offers to us two functions capable of realizing the above mentioned cross-check:

- checkdate (month, day, year); He verifies that the introduced date is correct.
- strtotime (cadena_fecha); He verifies that the chain of date is correct. For it the date must be in English format, that is to say, mm/dd/aa