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The actual effect of PHP's unset() function_PHP tutorial

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Jul 20, 2016 am 10:59 AM

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The actual effect of PHP’s unset() function

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The cost and release of memory by PHP variables, and whether unset() really releases the memory. Reposted from: The actual effect of PHP’s unset() function
The test code is as follows: Copy PHP content to clipboard

PHP code:

<font face="NSimsun"><span style="color: #007700">for ( <code id="code0" style="font-size: 12px"><font face="NSimsun"><span style="color: #007700">for ( </span><span style="color: #0000bb">$i </span><span style="color: #007700">= </span><span style="color: #0000bb">1</span><span style="color: #007700">; </span><span style="color: #0000bb">$i </span><span style="color: #007700"><span style="color: #0000bb">100</span><span style="color: #007700">; </span><span style="color: #0000bb">$i</span></span></font><font face="NSimsun"><span style="color: #007700">++ ) {<br>
        </span><span style="color: #0000bb">$str </span><span style="color: #007700">= </span><span style="color: #0000bb">str_repeat</span><span style="color: #007700">(</span><span style="color: #dd0000">'01234567'</span><span style="color: #007700">, </span><span style="color: #0000bb">$i</span></font><font face="NSimsun"><span style="color: #007700">);<br>
        </span><span style="color: #0000bb">$a </span><span style="color: #007700">= </span><span style="color: #0000bb">memory_get_usage</span></font><font face="NSimsun"><span style="color: #007700">();<br>
        unset(</span><span style="color: #0000bb">$str</span></font><font face="NSimsun"><span style="color: #007700">);<br>
        </span><span style="color: #0000bb">$b </span><span style="color: #007700">= </span><span style="color: #0000bb">memory_get_usage</span></font><font face="NSimsun"><span style="color: #007700">();<br>
        echo </span><span style="color: #dd0000">"n<br>" ></span><span style="color: #007700">.</span><span style="color: #0000bb">$i</span><span style="color: #007700">.</span><span style="color: #dd0000">': '</span><span style="color: #007700">.(</span><span style="color: #0000bb">$b </span><span style="color: #007700">- </span><span style="color: #0000bb">$a</span><span style="color: #007700">).</span><span style="color: #dd0000">' Bytes.'</span></font><font face="NSimsun"><span style="color: #007700">;<br>
}</span></font>

$i
=
1
;
$i
100
;
$i

++ ) {

$str
=
str_repeat
(
'01234567'
,
$i

);

$a
=
memory_get_usage

();
unset(
$str

);

$b
=
memory_get_usage

();
echo
"n
"
.
$i
.
': '
.(
$b
-
$ a
).
' Bytes.'

;
}

It can be seen from the results: 8 x 32 = 256 It is really necessary to release the memory when it is 256 bytes long. Some people say that it is faster than directly $str = null.
Here are the actual results:
The results are as follows:
1: 0 Bytes.
2: 0 Bytes.
3: 0 Bytes.
4: 0 Bytes.
5: 0 Bytes.
6: 0 Bytes.
7: 0 Bytes.
8: 0 Bytes.
9: 0 Bytes.
10: 0 Bytes.
11: 0 Bytes.
12: 0 Bytes.
13: 0 Bytes.
14: 0 Bytes.
15: 0 Bytes.
16: 0 Bytes.
17: 0 Bytes.
18: 0 Bytes.
19: 0 Bytes.
20: 0 Bytes.
21: 0 Bytes.
22: 0 Bytes.
23: 0 Bytes.
24: 0 Bytes.
25: 0 Bytes.
26: 0 Bytes.
27: 0 Bytes.
28: 0 Bytes.
29: 0 Bytes.
30: 0 Bytes.
31: 0 Bytes.
32: -272 Bytes.
33: -280 Bytes.
34: -288 Bytes.
35: -296 Bytes.
36: -304 Bytes.
37: -312 Bytes. 38: -320 Bytes. 39: -328 Bytes. 40: -336 Bytes. 41: -344 Bytes. 42: -352 Bytes. 43: -360 Bytes. 44: -368 Bytes. 45: -376 Bytes. 46: -384 Bytes. 47: -392 Bytes. 48: -400 Bytes. 49: -408 Bytes. 50: -416 Bytes. 51: -424 Bytes. 52: -432 Bytes. 53: -440 Bytes. 54: -448 Bytes. 55: -456 Bytes. 56: -464 Bytes. 57: -472 Bytes. 58: -480 Bytes. 59: -488 Bytes. 60: -496 Bytes. 61: -504 Bytes. 62: -512 Bytes. 63: -520 Bytes. 64: -528 Bytes. 65: -536 Bytes. 66: -544 Bytes. 67: -552 Bytes. 68: -560 Bytes. 69: -568 Bytes. 70: -576 Bytes. 71: -584 Bytes. 72: -592 Bytes. 73: -600 Bytes. 74: -608 Bytes. 75: -616 Bytes. 76: -624 Bytes. 77: -632 Bytes. 78: -640 Bytes. 79: -648 Bytes. 80: -656 Bytes. 81: -664 Bytes. 82: -672 Bytes. 83: -680 Bytes. 84: -688 Bytes. 85: -696 Bytes. 86: -704 Bytes. 87: -712 Bytes. 88: -720 Bytes. 89: -728 Bytes.90: -736 Bytes.
91: -744 Bytes.
92: -752 Bytes.
93: -760 Bytes.
94: -768 Bytes.
95: -776 Bytes.
96: -784 Bytes.
97: -792 Bytes.
98: -800 Bytes.
99: -808 Bytes.

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