What's the difference between echo, print, and print_r in PHP?_问答_开发者

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

I feel echo is a macro, and print_r is an alias开发者_如何学Go of var_dump.

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

print and echo are more or less the same; they are both language constructs that display strings. The differences are subtle: print has a return value of 1 so it can be used in expressions whereas echo has a void return type; echo can take multiple parameters, although such usage is rare; echo is slightly faster than print. (Personally, I always use echo, never 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, 0.0, 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] => 
)

echo

Outputs one or more strings separated by commas
No return value

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

print

Outputs only a single string
Returns 1, so it can be used in an expression

e.g. print "Hello"

or, if ($expr && print "foo")

print_r()

Outputs a human-readable representation of any one value
Accepts not just strings but other types including arrays and objects, formatting them to be readable
Useful when debugging
May return its output as a return value (instead of echoing) if the second optional argument is given

var_dump()

Outputs a human-readable representation of one or more values separated by commas
Accepts not just strings but other types including arrays and objects, formatting them to be readable
Uses a different output format to print_r(), for example it also prints the type of values
Useful when debugging
No return value

var_export()

Outputs a human-readable and PHP-executable representation of any one value
Accepts not just strings but other types including arrays and objects, formatting them to be readable
Uses a different output format to both print_r() and var_dump() - resulting output is valid PHP code!
Useful when debugging
May return its output as a return value (instead of echoing) if the second optional argument is given

Notes:

Even though print can be used in an expression, I recommend people avoid doing so, because it is bad for code readability (and because it's unlikely to ever be useful). The precedence rules when it interacts with other operators can also be confusing. Because of this, I personally don't ever have a reason to use it over echo.
Whereas echo and print are language constructs, print_r() and var_dump()/var_export() are regular functions. You don't need parentheses to enclose the arguments to echo or print (and if you do use them, they'll be treated as they would in an expression).
While var_export() returns valid PHP code allowing values to be read back later, relying on this for production code may make it easier to introduce security vulnerabilities due to the need to use eval(). It would be better to use a format like JSON instead to store and read back values. The speed will be comparable.

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() and var_dump() will echo by default, add a second argument to print_r() at least 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.

The difference between echo, print, print_r and var_dump is very simple.

echo

echo is actually not a function but a language construct which is used to print output. It is marginally faster than the print.

echo "Hello World";    // this will print Hello World
echo "Hello ","World"; // Multiple arguments - this will print Hello World

$var_1=55;
echo "$var_1";               // this will print 55
echo "var_1=".$var_1;        // this will print var_1=55
echo 45+$var_1;              // this will print 100

$var_2="PHP";
echo "$var_2";                   // this will print PHP

$var_3=array(99,98,97)           // Arrays are not possible with echo (loop or index  value required)
$var_4=array("P"=>"3","J"=>"4"); // Arrays are not possible with echo (loop or index  value required)

You can also use echo statement with or without parenthese

echo ("Hello World");   // this will print Hello World

print

Just like echo construct print is also a language construct and not a real function. The differences between echo and print is that print only accepts a single argument and print always returns 1. Whereas echo has no return value. So print statement can be used in expressions.

print "Hello World";    // this will print Hello World
print "Hello ","World"; // Multiple arguments - NOT POSSIBLE with print
$var_1=55;
print "$var_1";               // this will print 55
print "var_1=".$var_1;        // this will print var_1=55
print 45+$var_1;              // this will print 100

$var_2="PHP";
print "$var_2";                   // this will print PHP

$var_3=array(99,98,97)           // Arrays are not possible with print (loop or index  value required)
$var_4=array("P"=>"3","J"=>"4"); // Arrays are not possible with print (loop or index  value required)

Just like echo, print can be used with or without parentheses.

print ("Hello World");   // this will print Hello World

print_r

The print_r() function is used to print human-readable information about a variable. If the argument is an array, print_r() function prints its keys and elements (same for objects).

print_r ("Hello World");    // this will print Hello World

$var_1=55;
print_r ("$var_1");               // this will print 55
print_r ("var_1=".$var_1);        // this will print var_1=55
print_r (45+$var_1);              // this will print 100

$var_2="PHP";
print_r ("$var_2");                // this will print PHP

$var_3=array(99,98,97)             // this will print Array ( [0] => 1 [1] => 2 [2] => 3 ) 
$var_4=array("P"=>"3","J"=>"4");   // this will print  Array ( [P] => 3 [J] => 4 )

var_dump

var_dump function usually used for debugging and prints the information ( type and value) about a variable/array/object.

var_dump($var_1);     // this will print  int(5444) 
var_dump($var_2);     // this will print  string(5) "Hello" 
var_dump($var_3);     // this will print  array(3) { [0]=> int(1) [1]=> int(2) [2]=> int(3) } 
var_dump($var_4);     // this will print  array(2) { ["P"]=> string(1) "3" ["J"]=> string(1) "4" }

echo

Not having return type

print

Have return type

print_r()

Outputs as formatted,

Echo :

It is statement not a function No return value

Not Required the parentheses

Not Print Array

Print

It is real function

Return type 1

Required the Parentheses

Not Print Array

Print_r

Print in human readable format

String not in Quotes

Not Detail Information of Variable like type and all

var_dump

All dump information of variable like type of element and sub element

**Echocan accept multiple expressions while print cannot. The Print_r () PHP function is used to return an array in a human readable form. It is simply written as

![Print_r ($your_array)][1]

echo : echo is a language construct where there is not required to use parentheses with it and it can take any number of parameters and return void.

   void echo (param1,param2,param3.....);

   Example: echo "test1","test2,test3";

print : it is a language construct where there is not required to use parentheses it just take one parameter and return

    1 always.

           int print(param1);

           print "test1";
           print "test1","test2"; // It will give syntax error

prinf : It is a function which takes atleast one string and format style and returns length of output string.

    int printf($string,$s);

    $s= "Shailesh";
    $i= printf("Hello %s how are you?",$s);    
    echo $i;

    Output : Hello Shailesh how are you?
             27



   echo returns void so its execution is faster than print and printf

print_r() is used for printing the array in human readable format.

print_r() can print out value but also if second flag parameter is passed and is TRUE - it will return printed result as string and nothing send to standard output. About var_dump. If XDebug debugger is installed so output results will be formatted in much more readable and understandable way.

they both are language constructs. echo returns void and print returns 1. echo is considered slightly faster than print.