PHP version 5.6.12 code is as follows:
|
1
2
3
4
5
6
7
8
9
10
11
12
|
<?php
$arr
= [
'a'
,
'b'
,
'c'
,
'd'
,
'e'
];
foreach
(
$arr
as
$i
=>&
$a
) {
$a
=
$a
.
'_'
.
$a
;
echo
$a
.
'<br>'
;
}
echo
'<hr>'
;
foreach
(
$arr
as
$i
=>
$a
) {
echo
$a
.
'<br>'
;
}
echo
'<hr>'
;
print_r(
$arr
);
|
Output
Beginning to see the results of the second output foreach feeling very strange, how can output two d_d it?
Careful thought, the original because the PHP foreach $ a local variable scope is the entire function is still valid in the outer loop, rather than being enclosed within the loop,
So when $ a is not new variables when performing the second foreach, but still point to $ arr array address 5th element of reference,
When the second foreach actually stop to the 5th element array $ arr assignment in the cycle,
Specific assignment situation,
First: a_a assigned to the fifth element, the result is: [a_a, b_b, c_c, d_d, a_a]
Second: b_b assigned to the fifth element, the result is: [a_a, b_b, c_c, d_d, b_b]
Third: c_c assigned to the fifth element, the result is: [a_a, b_b, c_c, d_d, c_c]
Fourth: d_d assigned to the 5th element, the result is: [a_a, b_b, c_c, d_d, d_d]
Fifth: At this time, since the fifth element has become d_d again to d_d assigned to the 5th element, the result was to: [a_a, b_b, c_c, d_d, d_d]
Solution:
1. try not to use the same variable name loop;
2. After each use or use again unset ($ a) supra; treatment, release application address
foreach ($arr as $i=>&$a) {
$a
=
$a
.
'_'
.
$a
;
echo
$a
.
'<br>'
;
}
echo
'<hr>'
;
echo
$a
;
echo
'<hr>'
;
// 这里 unset 掉
unset(
$a
);
echo
$a
=
'ccc'
;
echo
'<hr>'
;
print_r(
$arr
);
echo
'<hr>'
;
foreach
(
$arr
as
$i
=>
$a
) {
echo
$a
.
'<br>'
;
}
echo
'<hr>'
;
print_r(
$arr
);
Output:
Now normal