What's the difference of echo,print,print_r in PHP?

Question

I use echo and print_r much,almost never use print.

I feel echo is a macro,and print_r is alias of var_dump.

But that's not the standard way to explain the difference.

Answer 1

print does the same thing as echo except echo is a language construct and not a real function so it's syntax is different. (For what it's worth, I've never used print.)

var_dump prints out a detailed dump of a variable, including its type and the type of any sub-items (if it's an array or an object). print_r prints a variable in a more human-readable form: strings are not quoted, type information is omitted, array sizes aren't given, etc.

var_dump is usually more useful than print_r when debugging, in my experience. It's particularly useful when you don't know exactly what values/types you have in your variables. Consider this test program:

$values = array(0, false, '');

var_dump($values);
print_r ($values);

With print_r you can't tell the difference between 0 and 0.0, or false and '':

array(4) {
  [0]=>
  int(0)
  [1]=>
  float(0)
  [2]=>
  bool(false)
  [3]=>
  string(0) ""
}

Array
(
    [0] => 0
    [1] => 0
    [2] => 
    [3] => 
)

Answer 2

Just to add to John's answer, echo should be the only one you use to print content to the page.

print is slightly slower. var_dump and print_r should only be used to debug.

Also worth mentioning is that print_r will echo by default, add a second argument that evaluates to true to get it to return instead, e.g. print_r($array, true)

The difference between echoing and returning are:

• echo: Will immediately print the value to the output
• returning: Will return the function's output as a string. Useful for logging, etc

Answer 3

echo

• No return value

• Outputs one or more strings separated by commas

  e.g. echo "String 1", "String 2"

print

• Returns 1, so it can be used in an expression

• Outputs only a single string

  e.g. if ((print "foo") && (print "bar"))

print_r()

• Outputs any variable (not just strings but even arrays, objects) as a formatted, human-readable string representation. Good for debugging. It's a more human-readable serialization than serialize().
• No return value, unless using the second optional argument, which causes it to return a string containing what would have been output instead of outputting it.

Notes:

• Whereas echo and print are language constructs, print_r() is a function. This means that using parantheses to enclose the arguments for echo and print can behave in unintuitive ways sometimes.