Here is a list of the different formatting codes passed to strftime :. You want to extract the date and time from a string such as and convert it into a usable form such as seconds since the UNIX epoch began. You're probably saying as I once did that finding the number of seconds since the UNIX epoch began on January 1, is not really that helpful. However, I contend that it helps you in a great many things. For example, in recipe 3.
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In recipe 3. So, finding the epoch seconds from a user-submitted string is extremely useful when doing any type of conversions with time. Then we call the mktime function, which returns the number of seconds since January 1, , and our conversions are complete. As an easter egg, PHP also has a built-in function, strtotime , that will try to figure out the format of the date in the input string and return a timestamp for it. You can omit parts of the date, such as "May 2" and strtotime will use the current date and time for the remainder.
Here is an example:. You can use it, for example, to find out what the date will be 40 days from some starting date:. The relative offset can be positive or negative and can be seconds, minutes, hours, days, months, and years. You can even combine it, like so:.
Use the microtime function to find the time in seconds and microseconds before and after your snippet is run:. This code reports the time difference between using a while loop and using a for loop the while loop is the faster of the two.
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The solution not the code for testing whether a while loop was faster than a for loop could have been slimmed down to the following:. This is known as epoch seconds , and is equal to the number of seconds since January 1, We assign this value to the first time, execute the code that we want to benchmark, and then calculate the microtime again. If you are timing two different code segments in one script, you should use the unset function between the different timings see the solution for an example of this.
That way you don't have any extra memory set aside for those variables when you run the second portion of your script. If you find yourself benchmarking your code execution often, you can make use of this handy function contributed by someone on the PHP mailing list formatted slightly :. As this book was being released two new classes came out at Pear. They were authored by Sebastian Bergmann of phpOpenTracker. Use PHP's sleep and usleep functions, depending on how long you want your program to stop execution:.
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The sleep and the usleep functions both make system calls to the sleep function. However, the usleep function converts the sleep time, like so:. Sleeping is sometimes useful if you are working with sockets, or you are writing a daemon CGI version of PHP only that performs operations at regular intervals of time. This usually can and should be done with cron Manipulating Strings. Dissecting Strings. Using the Ternary Operator. Swapping Variables.
Splitting a String by Characters. Reversing Parts of a String. Converting the Case of a String. Removing Whitespace from a String. Escaping Special Characters in a String. Reading a Comma-Delimited Text File.
Parsing a URL. Fuzzy Matching.
Creating a Unique Identifier. Encrypting a String. Converting Between Cyrillic Character Sets. Working with Numbers, Dates, and Times. Working on a Series of Numbers. Rounding Arbitrary-Precision Numbers. Converting Numbers Between Different Bases. Finding the Log of a Number. Finding the Binary Representation of a Number. Converting Between Arabic and Roman Numerals. Validating Credit Card Numbers.
Formatting Numbers. Converting Between Radians and Degrees. Calculating Cosines, Sines, and Tangents. Generating Random Numbers. Generating Unique Random Numbers. Weighting Random Numbers. Loading Today's Date into an Array. Checking the Validity of a Date. Determining Date Intervals.
Finding the Date and Time for Different Locales. Formatting Timestamps. Parsing Dates and Times from Strings. Performing Benchmarks. Halting Program Execution. Using Arrays. Declaring an Array. Printing Out an Array.
Eliminating Duplicate Elements. Enlarging or Shrinking an Array. Merging Arrays. Iteratively Processing Elements in an Array. Accessing the Current Element in an Array. Accessing Different Areas of an Array. Searching an Array. Searching for the Different Elements in Two Arrays. Randomizing the Elements of an Array.
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Sorting an Array. Sorting Sensibly. Reversing Order. Perl-Based Array Manipulation Features. Working with File Constants. Working with PHP Globals. Matching Data with Regular Expressions. Assigning the Results of a Pattern Replacement.