PHP Strings

String type data is collection of any number of characters or bytes (In computer memory, different combination of eight bits, 0 or 1, makes a byte and express characters) enclosed with string notation.  These characters include letters, numbers, symbols, spaces, and variables.

Creating strings

There are four ways to create strings in PHP-

1. Single quote
2. Double quote
3. Heredoc syntax
4. Nowdoc syntax

Single quote

• In this method, characters are enclosed with single quotation mark (‘).
• Contents inside the single quotes are displayed as it is.
• Variables inside the single quotes are not interpreted.
• Special characters insides don’t express the meanings.

Example

<pre>
<?php
    $month_quantity=12;
    echo ‘There are $month_quantity months. \n January is the first one.';
?>
</pre>

Output:
There are $month_quantity months. \n January is the first one.

In the output above, the value of the variable $ today is not printed and the special character new line \n has no effect on output.

Double quote

• It is the most commonly used quote to express string.
• Here characters are enclosed with double quotation marks (” “).
• PHP interpreter interprets variables and special characters inside double quotes. In the following example, the above example is re-written using double quotes.

Example

<pre>
<?php
    $month_quantity =12;
    echo “There are $month_quantity months. \nJanuary is the first one.”
?>
</pre>

Output:
There are 12 months.
January is the first one.

Don’t mix single quote and double quote in a string pair-

If a string starts with a single quote, then it must end with a single quote. Similarly, if a string starts with a double quote, it must end with a double quote. If single is mixed with double quote in a string, PHP will produce a syntax error.

<?php
    echo ‘This string is surrounded by single quotes only.’; //It is correct;
    echo “This string is surrounded by double quotes only.”; //It is correct;
    echo ‘This string is surrounded by a single and a double quotes.”; //It will display a syntax error;
 ?>

How to display single quote and double quote in a string?

Sometimes you’ll need to use single quote in your string (ex. John’s blog). Similarly, you may need to display double quote in a string too. There are 2 ways to do these-

1. To display a single quote (apostrophe), the string could be within double quotation makes. Like the following example-

   <?php
       echo “It is John’s blog.”;  // Output: It is John’s blog.
   ?>

   Similarly, to display double quote, the string could be surrounded by single quotes, Check the following example-

   <?php
    echo ‘John said “This is my car”.’;  // Output: John said " This is my car ".
   ?>

2. If you want to display a double quote within a double quoted string, precede the middle double with a backslash. Check the following example-

   <?php
       echo “John said \“This is my car\”.”;  // Output: John said "This is my car".
   ?>

   You can apply the same rule in a single quoted string too-

   <?php
       echo ‘John said \’This is my car\’.’;  // Output: John said "This is my car".
   ?>

Heredoc syntax

• The third way of creating string is to use here-document or in short heredoc syntax.
• When large amount of texts need to be displayed, then heredoc is the choice.
• It works similarly to double quotes except it doesn’t require escaping quotes, but the escaping codes in the table above can be used.

Rules of using heredoc syntax

• Heredoc syntax begins with three less than signs (<<<) followed by a user defined name. The name can be any combination of letters, numbers, underscores but the first character must be a letter or an underscore.
• The string begins in the next line and goes as long as it requires
• After the string, the same exact name that is defined after the (<<<) signs in the first line should be placed in the next line. Nothing can be added in this last line except a semicolon after the name and it is optional.

Example:

<pre>
<?php
    echo <<<EOD
        This is first line. \nThis is second line.;
EOD;
?>
<pre>

Output:
This is first line.
This is second line.

Nowdoc syntax

• If heredoc syntax works similar to double quote, then nowdoc syntax works similar to single quote.
• Like single quote, no variable inside the nowdoc is interpreted.

Rules of using nowdoc syntax

Nowdoc supports all the syntax rules of heredoc except the starting name; it must be enclosed by single quotes.

Example:

<pre>
<?php
    echo <<<’EOD’
        This is first line. \nThis is second line.;
EOD;
?>
<pre>

Output:
This is first line. \nThis is second line.

What is escaping character?

You’ve seen to display a quote how backslash is used. This is known as escape the character to the string. This tells PHP interpreter to print the character as it is. When you’re escaping a quotation mark, PHP interpreter doesn’t consider it as the beginning/ending of the statement.

Which characters can be escaped?

• In a single quoted string, PHP only escapes single quote (‘) and backslash (\).
• In a double quoted string, PHP escapes double quote (“) and backslash (\).
  The following few sequences support different strings format-

  Sequence	Meaning	Support
  \’	Single quote	Only single quote
  \”	Double quote	Only double quote
  \\	Backslash	All strings but nowdoc

• Escaping other characters in double quoted string and heredoc string express special meaning.
• All the following escape sequences have special meaning and can be used in only double quoted and heredoc strings –
  

  Sequence	Meaning
  \n	New line
  \r	Carriage return
  \t	Horizontal tab
  \v	Vertical tab
  \e	Escape
  \f	Form feed
  \[0-7]{1,3}	Octal value
  \x[0-9A-Fa-f]{1,2}	Hexadecimal value

  Example
  Check the example-

  <pre>
  <?php
      echo "This is first line \nThis is second line.";
  ?>
  <pre>

  Output-
  This is first line
  This is second line.

  [To show the output of the escape sequences, HTML tag <pre> is used in the previous examples.]

Variable parsing

When variable is included inside double quoted string or heredoc string, the variable is parsed or interpreted. There are 2 ways to include variables inside double quoted string or heredoc string.

1. Simple syntax and
2. Complex syntax

Simple syntax

• In this way, a variable is simply put inside the string.
• When php parser finds the $ sign, it treats it as the starting of a variable.
• Variables that represent scalar type, array, or object type data are parsed.

  <?php
      //  Parsing scalar type data
      $today = “Tuesday”;
      echo “This is $today today.”;  // output: It is Tuesday today.
  
      // Parsing array type data
      $days=[“Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”, “Saturday”, “Sunday”];
      echo “This is $day[1] today.”;  // This is Tuesday today.
  
      // Parsing object type data
      class days{
          public $today = “Tuesday”;
      }
      $days = new days();
      echo “This is $days->today today.”;  // This is Tuesday today.
  ?>

Complex Syntax

• Here variable is wrapped with { and }.
• When php parser finds the {$ sign, it treats it as the starting of a variable. Please make sure that { immediately follows $ in the syntax.
• Variables that represent scalar type, array, or object type data are parsed.

  <?php
      //  Parsing scalar type data
      $today = “Tuesday”;
      echo “This is {$today} today.”;  // output: It is Tuesday today.
  
      // Parsing array type data
      $days=[“Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”, “Saturday”, “Sunday”];
      echo “This is {$day[1]} today.”;  // This is Tuesday today.
  
      // Parsing object type data
      class days{
          public $today = “Tuesday”;
      }
      $days = new days();
      echo “This is {$days->today} today.”;  // This is Tuesday today.
  ?>

  

  Curly braces makes it very clear that which one is variable and which parts are static in string.