Difference between PHP if $variable, isset(), empty(), strlen()

What is the difference between PHP functions below ?

if ($variable) { }
if (isset($variable)) { }
if (!empty($variable)) { }
if (strlen($variable)) { }

Hi,

The differences between those PHP functions are visible in specific cases. For example when variable is created, is NULL, is 0, is TRUE or FALSE etc.

In the condition if ($variable) { echo "OK"; } the output will be OK when $variable:

• is not empty
• is TRUE
• is not FALSE
• is not 0
• is not NULL

In the condition if (isset($variable)) { echo "OK"; } the output will be OK when $variable:

• is set and is different from NULL

In the condition if (!empty($variable)) { echo "OK"; } the output will be OK when $variable:

• is not empty
• is TRUE
• is not FALSE
• is not 0
• is not NULL

In the condition if (strlen($variable)) { echo "OK"; } the output will be OK when $variable:

• is not empty
• is TRUE
• is not FALSE
• is not NULL

In relation to these functions, you can use is_null() to find out if variable is NULL.