Eight days in and I’m still only dealing with the basics.  Today is all about Strings – Comparing, Searching and Replacing data.  There are a good amount of tricks in here, especially when converting strings to numbers and vice-versa.  Time to pay attention and take notes!

Comparison

• When doing a string comparison to a number, be aware that PHP will attempt to convert the string to a number.  This is done by reading character by character until it cannot equal a number.  For example: "123abc" = 123 and "0x23bo" = 0x23b.  If PHP cannot figure something out, it equates as 0: "abc" = 0.
• This conversion can be avoided by using the triple-equal sign (===) to force type comparison first.
• String comparison is also possible with two functions: strcmp($str1, $str2) and strcasecmp($str1, $str2).  These are identical in operation with the exception of the second function ignores case.  Both will return 0 indicating the strings are equal, <0 if $str1 is alphabetically less than $str2, >0 if $str1 is alphabetically higher than $str2.
• Additionally, you can use strncasecmp($str1, $str2, $len) to compare first $len characters of case-insensitive strings.

Searching

• When searching strings, there are usually two types of functions.  Simple (fast) and Complex (slow).  As an example, to search a string for characters, you can quickly use strpos($string, $word).  It’s fast and will return either false (check using ===) if not found or the starting position of that $word.
• There is, conversely, a more complex version, strstr($string, $word) which returns the text from that point on.
• Both functions have optional parameters to tell where to start looking, strpos($string, $word, $starting).
• And there are case-insensitive versions of both: stripos and stristr.
• While the previous functions were basic searching, there is another type called "masking."  This searches a string for the largest run of characters matching a specified set (whitelist) or outside a specified set (blacklist).  The strspn($string, $mask) function performs the whitelist version while the strcspn($string, $mask) is the blacklist one.
• Both have two optional parameters to specify where to start searching and how many characters to look at.
• There is a HUGE section (tomorrow) on Regular Expressions, so this isn’t it (don’t worry).

Replacing

• The basic find and replace function is str_replace($from, $to, $string). 
  Personal Note: it is really annoying how often function parameters are rearranged between similar functions.
• This function can take (alternately) arrays instead of strings for $from and $to.
• There is also a case-insensitive version (what a surprise) called str_ireplace().
• To replace text from a certain point in a string, you can use substr_replace($string, $replacement, $start, [$length]) with $length being an optional parameter limiting the amount that can be changed.
• Finally there is substr($string, $start, [$len]), designed to extract a portion of text from $string starting at $string with optional $len length.  This has a very useful feature: $start values that are negative will be the length of the string – $start.

I can’t read/write that much more tonight, too busy!  I need to do this stuff earlier in the day (ugh, I need more free time).  Tomorrow is string formatting and regular expressions (woof).