A string in PHP is a variable holding zero or more characters of text, and can be used to store words or sentences to be inserted into the body of a web-page, or to be used in the result of calculations. Strings are specified by wrapping a section of text in single or double quotes. Here are some examples of valid string variables.
$str1 = "This is a string"; $str2 = 'This also works'; $str3 = "Splitting strings between lines is also acceptable";
Here are some considerations to bear in mind when assigning strings
- The start and end quotes must be of matching types - you cannot mix single and double quotes. This code is invalid
$str1 = "This code will break';
If you’re using single or double quotes within the string itself, this can cause complications. Take the following as an example
$str1 = 'Don't use unescaped quotes'; /* this will break */
Here, the use of the single quote within the string makes PHP think you’re terminating the string after “Don”, and then it expects a semicolon directly after. In this case, the sentence continues and so the code breaks.
A solution to this is to escape the offending character. This is done via the use of the backslash (\) character immediately before. Like so
$str1 = 'Don\'t use unescaped quotes'; /* this is now valid code */
This tells PHP to treat the single quote as if it were a character to be printed, rather than an element of the PHP syntax to be processed.
You will also encounter this problem if you try and use the dollar ($) symbol inside strings. Because of the way PHP allows variables to be inserted into strings (and this will be explained further shortly), PHP will interpret any use of the dollar symbol as an attempt to insert a variable. Note that this only happens when using double quotes. For example
$string = "Hello world"; $str1 = "$string"; /* will output - Hello world */ $str2 = "\$string"; /* will output - $string */
Escaping characters can be very useful, but if you’re using a large number of quotes and other symbols inside a string, things can get confusing. There is an alternative way to specify strings
Heredoc syntax is a way to write large sections of text in PHP without the need to worry about escaping quotes. Strings are expressed in this way as follows
- An initial opening delimiter consisting of three “Less than” symbols (<<<) and a string of your choice - it doesn’t matter what you choose as long as you follow the naming rules for variables (letters, numbers and underscores. The first character cannot be a number
- On a new line start your string content. This can run onto as many new lines as you like and contain as much content as you require
- When you wish to terminate a new string, on another new line, place your chosen string followed by a semicolon. This must be the only text on the line (not even comments are allowed) and must not be indented
Here is an example
$string = <<<STRINGHERE This is a Heredoc syntax string. It's very useful indeed STRINGHERE;
And this produces
This is a Heredoc syntax string. It's very useful indeed
Here is an example of a faulty Heredoc string
$string = <<<STRINGHERE This is a Heredoc syntax string. It's very useful indeed. But this one is broken STRINGHERE; //see the indentation? //there should be no comment on the previous line either
PHP includes some powerful methods to combine strings with ease, including the ability to quickly join strings together, and the ability to insert other variables into strings.
Variables can be inserted into strings in one of three ways
- Using the dot (.) operator to concatenate strings and variables. Take the following code
$a = "This is "; $b = "an example of "; $c = $a.$b."the dot operator"; echo $c;
this produces
This is an example of the dot operator
- By placing the variable directly into the sentence
$a = "This is "; $b = "an example of "; $c = "$a$b variable/string insertion";
This example will only work when using double quotes or Heredoc syntax, strings defined using single quotes do not possess this functionality.
In this example, we have placed the variable names $a and $b directly into the string. This is a quick and easy way of printing variable names into strings, but you must bear in mind…
You must make sure to have a space after a variable name and any following text
For more complex variables such as arrays (outlined later), their more complex syntax requires that you surround them in braces e.g.$array = array(); $array["var"] = "This is an array "; $string = "{$array["var"]} inserted into a string"; echo $string;
Giving us
This is an array inserted into a string
- When using the echo statement only, variables can be joined together by placing commas between them. This is actually a slightly faster way of printing multiple variables than with the dot operator, but the difference is negligible except for when performing millions of these operations
$a = "An example of "; $b = "joining variables "; echo $a,$b,"together with commas";
Giving us
An example of joining variables together with commas
Note that the following code is invalid, since this method only works with echo
$a = "An example of "; $b = "joining variables "; print_r ($a,$b,"together with commas"); //invalid $c = $a,$b,"together with commas"; //invalid
