The PHP Function Is_string()

The is_string() PHP function is used to check if a type of variable is a string. A string is a data type, such as floating point or integer, but it represents text rather than numbers. A string uses a set of characters that includes spaces and numbers. For instance, an address such as "1234 Broadway" and the sentence "I ate 3 hotdogs" contain numbers that should be treated as text, not as numbers.

How to Use the Function

Is_string is used within an if () statement to treat strings in one way and non-strings in another. It returns true or false. For example:

<?php 
if (is_string(23)) 
{
echo "Yes";
} else {
echo "No";
}
?>

The code above should output "No" because 23 is not a string. Let's try this again:

<?php 
if (is_string("Hello World")) 
{
echo "Yes";
} else {
echo "No";
}
?>

Since "Hello World" is a string, this would echo "Yes."

Specifying a String

A string can be specified in four ways:

• Single quoted
• Double quoted 
• Heredoc syntax
• Nowdoc Syntax

Each of these methods requires strict adherence to PHP rules, which are available at the PHP website. The simplest method, single-quoted strings, requires special treatment when literal single quotation marks or literal backslashes appear in the string. Include a backslash in front of the single quotation mark or backslash within the string. The example below illustrates this treatment:

<?php
// Outputs: Arnold said: "I'll be back"
echo 'Arnold said: "I\'ll be back"';
// Outputs: I deleted C:\*.*?
echo 'I deleted C:\\*.*?';
?>

Similar Functions

• is_float() – determines if the type of variable is float
• is_int() – determines if the type of variable is integer
• is_bool() – determines if a variable is a boolean
• is_object() – determines if a variable is an object
• is_array() – determines if a variable is an array
• is_numeric() – determines if a value is a number or a numeric string