print_r is terrible
2014/07/2816:22 UTC
The short version: use var_dump, don’t use print_r.
print_r is to print human readable representations of a variable’s contents.
It is practically useless as a debugging tool. It isn’t even useful for
humans to consume it because no human wants to read arrays or even think about
the concept of arrays.
On first glance it kind of works.
php > print_r('foo bar');
foo bar
php > print_r([1, 2, 3]);
Array
(
[0] => 1
[1] => 2
[2] => 3
)Those sure are some fantastic string representations of things.
But you quickly find out that many things are printed as being the same value.
php > print_r([false, '', null]);
Array
(
[0] =>
[1] =>
[2] =>
)
php > print_r([0, 0.0, '0'])
Array
(
[0] => 0
[1] => 0
[2] => 0
)
php > print_r([true, 1, '1']);
Array
(
[0] => 1
[1] => 1
[2] => 1
)When strings are involved, you also can get output that may look the same but isn’t because of whitespace or other various non-visible characters.
php > print_r(['foo ', 'foo', "foo" . chr(0)]);
Array
(
[0] => foo
[1] => foo
[2] => foo
)..Or you get things caused by people who just want to watch the world burn.
php > print_r([["Array\n\t\t(\n\t\t\t[0] => Wello\n\n\t\t)\n"]]);
Array
(
[0] => Array
(
[0] => Array
(
[0] => Wello
)
)
)
php > $a = print_r([0], true);
php > print_r($a);
Array
(
[0] => 0
)print_r does not display data in any structured manner and sacrifices
differentiating between types for the sake of readability. While you are
debugging you don’t want readability. You want to know what the variable
contains. var_dump gets you that.
php > var_dump(['foo ', 'foo', "foo" . chr(0)]);
array(3) {
[0] =>
string(4) "foo "
[1] =>
string(3) "foo"
[2] =>
string(4) "foo\000"
}
php > var_dump([0, 0.0, '0']);
array(3) {
[0] =>
int(0)
[1] =>
double(0)
[2] =>
string(1) "0"
}