intval()

(PHP 4, PHP 5, PHP 7)

获取变量的整数值

说明

intval(mixed $var[,int $base= 10]): int

通过使用指定的进制$base转换（默认是十进制），返回变量$var的integer数值。intval()不能用于 object，否则会产生E_NOTICE错误并返回 1。

参数

$var

要转换成 integer 的数量值

$base

转化所使用的进制

Note:

如果$base是 0，通过检测$var的格式来决定使用的进制：

• 如果字符串包括了"0x"(或"0X")的前缀，使用 16 进制(hex)；否则，
• 如果字符串以"0"开始，使用 8 进制(octal)；否则，
• 将使用 10 进制(decimal)。

返回值

成功时返回$var的 integer 值，失败时返回 0。空的 array 返回 0，非空的 array 返回 1。

最大的值取决于操作系统。 32 位系统最大带符号的 integer 范围是-2147483648 到 2147483647。举例，在这样的系统上，intval('1000000000000')会返回 2147483647。64 位系统上，最大带符号的 integer 值是 9223372036854775807。

字符串有可能返回 0，虽然取决于字符串最左侧的字符。使用整型转换的共同规则。

范例

Example #1intval()例子

下面的例子运行于 32 位系统上。

<?php
echo intval(42);                      // 42
echo intval(4.2);                     // 4
echo intval('42');                    // 42
echo intval('+42');                   // 42
echo intval('-42');                   // -42
echo intval(042);                     // 34
echo intval('042');                   // 42
echo intval(1e10);                    // 1410065408
echo intval('1e10');                  // 1
echo intval(0x1A);                    // 26
echo intval(42000000);                // 42000000
echo intval(420000000000000000000);   // 0
echo intval('420000000000000000000'); // 2147483647
echo intval(42, 8);                   // 42
echo intval('42', 8);                 // 34
echo intval(array());                 // 0
echo intval(array('foo', 'bar'));     // 1
?>

注释

Note:

除非$var是一个字符串，否则$base不会起作用。

更新日志

参见

• boolval() 获取变量的布尔值
• floatval() 获取变量的浮点值
• strval() 获取变量的字符串值
• settype() 设置变量的类型
• is_numeric() 检测变量是否为数字或数字字符串
• 类型转换的判别
• BCMath 任意精度数学函数

Not mentioned elsewhere: intval(NULL) also returns 0.

It seems intval is interpreting valid numeric strings differently between PHP 5.6 and 7.0 on one hand, and PHP 7.1 on the other hand.
<?php
echo intval('1e5');
?>
will return 1 on PHP 5.6 and PHP 7.0,
but it will return 100000 on PHP 7.1.

Be careful :
<?php
$n="19.99";
print intval($n*100); // prints 1998
print intval(strval($n*100)); // prints 1999
?>

intval converts doubles to integers by truncating the fractional component of the number.
When dealing with some values, this can give odd results. Consider the following:
print intval ((0.1 + 0.7) * 10);
This will most likely print out 7, instead of the expected value of 8.
For more information, see the section on floating point numbers in the PHP manual (http://www.php.net/manual/language.types.double.php)
Also note that if you try to convert a string to an integer, the result is often 0.
However, if the leftmost character of a string looks like a valid numeric value, then PHP will keep reading the string until a character that is not valid in a number is encountered.
For example:
"101 Dalmations" will convert to 101
"$1,000,000" will convert to 0 (the 1st character is not a valid start for a number
"80,000 leagues ..." will convert to 80
"1.4e98 microLenats were generated when..." will convert to 1.4e98
Also note that only decimal base numbers are recognized in strings.
"099" will convert to 99, while "0x99" will convert to 0.
One additional note on the behavior of intval. If you specify the base argument, the var argument should be a string - otherwise the base will not be applied.
For Example:
print intval (77, 8);  // Prints 77
print intval ('77', 8); // Prints 63

Here is a really useful undocumented feature:
You can have it automatically deduce the base of the number from the prefix of the string using the same syntax as integer literals in PHP ("0x" for hexadecimal, "0" for octal, non-"0" for decimal) by passing a base of 0 to intval():
<?php
echo intval("0x1a", 0), "\n"; // hex; prints "26"
echo intval("057", 0), "\n"; // octal; prints "47"
echo intval("42", 0), "\n"; // decimal; prints "42"
?>

You guys are going to love this. I found something that I found quite disturbing.
$test1 = intVal(1999);
$amount = 19.99 * 100;
$test2 = intVal($amount);
$test3 = intVal("$amount");
echo $test1 . "<br />\n";
echo $test2 . "<br />\n";
echo $test3 . "<br />\n";
expected output:
1999
1999
1999
actual output
1999
1998
1999
Appears to be a floating point issue, but the number 1999 is the only number that I was able to get to do this. 19.99 is the price of many things, and for our purpose we must pass it as 1999 instead of 19.99.

<?php
echo intval("10 days");     //10
echo intval("days 10");     //0
?>

The binary notation is NOT supported until php7.2
<?php
             // PHP <7.2 | PHP >=7.2
echo intval(0b11);    //  3   |   3
echo intval(-0b11);   //  -3   |  -3
echo intval('0b11');   //  0   |   0
echo intval('-0b11');  //  0   |   0
echo intval('0b11', 0); //  0   |   3
echo intval('-0b11', 0); //  0   |  -3
?>

if you want to take a number from a string, no matter what it may contain, here is a good solution:
<?php
function int($s){return(int)preg_replace('/[^\-\d]*(\-?\d*).*/','$1',$s);}
echo int('j18ugj9hu0gj5hg');
//output: 18
?>
this example returns an int, so it will follow the int rules, and has support for negative values.
<?php
function int($s){return($a=preg_replace('/[^\-\d]*(\-?\d*).*/','$1',$s))?$a:'0';}
echo int('j-1809809808908099878758765ugj9hu0gj5hg');
//output: -1809809808908099878758765
?>
this one returns a string with just the numeric value.
it also supports negative values.
the latter is better when you have a 32 bit system and you want a huge int that is higher than PHP_MAX_INT.

Sometimes intval just won't cut it. For example if you want to use an unsigned 32-bit int and need all 32 bits. Recently, I wrote a little script that took and integer and converted it to an IP address. After realizing I couldn't just mod the whole thing, since the sign bit throws it off (and compensating for that), we ran into a problem where if it was entered into a form, the value somehow wasn't converted to an integer properly, at least not implicitly. The solution for this, and the way I recommend converting a string to an integer, is:
$num = $num + 0;
and PHP will leave your number alone; it'll just know it's a number. Such is the fun of a loosely-typed language. :)

As addendum, the "if ($int > 0)" check in the encode function is redundant. It doesn't do anything bad to keep it in since it will always be true when reaching that point, but it's a meaningless conditional this way. It's a remnant from when I tried to write the function in terms of bitshifts, which could lead to negative ints when shifting if the 32nd bit was set (instead of always padding with 0's when using >> it pads with 1's leading to negative ints).

Do not use intval() when you really want round(). This is due to how PHP handles precision. 
echo number_format(8.20*100, 20), "<br />";
echo intval(8.20*100), "<br />";
echo floor(8.20*100), "<br />";
echo round(8.20*100), "<br />";
819.99999999999988631316
819 
819
820

The behaviour of intval() is interesting when supplying a base, and you better check your intval base-based expressions, as it is counter-intuitive.
As the example shows
<?php
 intval('42', 8); // => 34
 intval(42, 8);  // => 42 !
?>
PHP considers the 42 as being already an integer, and doesn't apply any conversion. And supplying
<?php
 intval(49, 8); // => 49 !
?>
produces no error and no warning.

Still have on mind, that if you convert big numbers by adding zero, PHP makes automatic "to a float" conversion, so it is same as floatVal(). So if the number is realy big (over 13 digits), you can lose preciosity. Do not use it for such long numbers, if all bits do matter (IPv6 addresses and similar).

The example is wrong for PHP 7.1
intval('1e10') does not return 1 as the example states, it returns 10000000000. This has broken at least one library I know of (BEncodeLib).

beware:
<?php
  // observe the following
  echo intval( strval( -0.0001 ) ); // 0
  echo intval( strval( -0.00001 ) ); // -1
  // this is because
  echo strval( -0.0001 ); // -.0001
  echo strval( -0.00001 ); // -1.0E-5
  // thus beware when using
  function trunc2_bad( $n ) {
   return intval( strval( $n * 100 ) / 100 );
  }
  // use this instead
  function trunc2_good( $n ) {
   return intval( floatval( strval( $n * 100 ) ) / 100 );
  }
?>

Rob_Kohr at no_need_to_email dot me dot com
11-Nov-2002 12:24   
[snip]
$var=intval("122.5");
//$var==122
This is nice if you want to turn a double into an int automatically rounding down
Hum, I had a bug earlier today, involving ===. Coming from a c++ background, I can't help testing for types. I was using floor() to get an integer from a division by 2, and comparing that to a known integer from a for loop. Well, first I changed the === to == because the test would always be false otherwise. Next, I looked up this function, and converted most of my floor() calls to intval() calls, because I really meant to get an int, and not a float with no decimal part. So I have to disagree with the editor note here. Oh, and I'm comfortably back to using ===.

Re: nobodyisperfect88 at hotmail dot de
jay at w3prodigy dot com had it right. I believe it is an issue with the floating point registers on computers, which have a precision of about 17 digits. When you get more precise than that, it rounds.
Since the second example can fit in the register, no rounding occurs, and PHP can truncate the portion after the decimal. However, the system automatically rounds the first example to 1, which is what PHP returns.
(Tested on Windows XP 32bit)

I just wanted to be sure that a string was going to be valid if I intval'ed it. This regular expression matches:
0
Any positive integer (no + sign)
Any negative integer (with a - sign)
It does not match a leading 0 or any other character. You are advised to strip out commas, trim the string and check range yourself ;)
<?php
/**
 * Loops through each non-array element and actions a function.
 *
 * @return boolean|integer TRUE if the value matches as an integer, FALSE if
 * an error occured or 0 if not match was found.
 */
public function validate($value)
{
  $value = preg_match('/^(0|(-{0,1}[1-9]\d*))$/', trim($value));
  if ($value == 1)
    return true;
  else
    return $value;
}
?>
If you use intval() now, you are merely changing the data type.

re: Disturbing issue with intval()
It's probably just good practice to round decimals anyways. i.e...
$amount = round(19.99 * 100);
$test2 = intVal($amount);
$test3 = intVal("$amount");
echo $test2 . "<br />\n";
echo $test3 . "<br />\n";

If you need the reverse function of intval(), the code hereunder might be helpfull.
<?php
function itoa( $ii, $radix=10, $stritoa="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabc" ) {
  if ( $radix > strlen( $stritoa ) )  //  does request makes sense?
    return "";  //  think of your own way to handle this case
  $sign = $ii<0 ? "-": "";
  $ii = abs( $ii );
  $rc = "";
  do {
    $rc .= $stritoa[ $ii % $radix ];
    $ii = floor( $ii / $radix );
    } while ( $ii >0 );
  return $sign . strrev( $rc );
  }
?>

Since integers are stored on multiple bytes in the memory in binary format, once an signed long integer reaches the maximum value of 2147483646 (which is the maximum value that 8 bits of memory, size of a long int, can store, binary-wise), atleast on C/C++ the number starts to roll back, going gradually to ...45, ...45 and eventually reaching a negative value. Some REALLY large values will return -1, probably because PHP simply rejects the number, though I'm not sure why.
For further info:
http://www.rwc.uc.edu/koehler/comath/13.html

When you need to work with integer values that exceed maxint, the following functions may be of use to you - they form a codec pair for integers of variable length rather than fixed length, encoded in a byte as a 7 bit numberal with a 1 bit has-more flag, indicating that the next byte encodes a higher order part of the same number still.
<?php
/* encode integer as 7bit with has-more bit numeral,
  ordered lowest byte first. */
function encode_7bhm($int) {
 if ($int==0) return chr(0); // shortcut
 $ret = "";
 while($int != 0) {
  $high = floor($int / 128);   // overflow for this round
  $low = $int - ($high * 128); // 7 bit numeral
  if ($int > 0) {
   if ($high > 0) { $low = $low + 128; } // has-more flag
   $ret .= chr($low); } //encode
  $int = $high; // set overflow as next round's number
 }
 return $ret;
}
/* decode a 7bit with has-more bit numeral,
  ordered lowest byte first. */
function decode_7bhm($hmb) {
 $ret = 0;
 $pos = 0;
 $high = 1;
 while($high == 1) {
  $byte = ord(substr($hmb, $pos, 1));
  $high = floor($byte/128); // gets has-more flag
  $low = $byte - ($high*128);
  $ret += $low * pow(128, $pos++); // decode
 }
 return $ret;
}
?>
This codec pair is also quite useful when needing to write ints to files, as this is a low-numeral biased encoding: most of the time this will only require 8 or 16 bit rather than the 32 bits an int will use in fixed-length encoding.
The encoding range:
 1 byte - 0 through 128 (2^7)
 2 bytes - 129 through 16,384 (2^14)
 3 bytes - 16,385 through 2,097,152 (2^21)
 4 bytes - 2,097,153 through 268,435,456 (2^28)
while indeed a 32 bit encoded variable length integer will be lower than maxint, rather than needing a new 32 bit block to represent higher range only 8 more bits are required to represent this higher number (for completeness the range of representation by bytes 5-8 are listed):
 5 bytes - 268,435,457 through 34,359,738,368 (2^35)
 6 bytes - 343,59,738,369 through 4,398,046,511,104 (2^42)
 7 bytes - 4,398,046,511,105 through 562,949,953,421,312 (2^49)
 8 bytes - 562,949,953,421,313 through 720,57,594,037,927,936 (2^56)
Also for completeness, the function to read a 7 bit with has-more bit from a filepointer:
<?php
// read a 7bhm numeral from file
function read_7bhm($fp) {
 $bytestring = "";
 $high = 1;
 while($high==1) {
  $byte = fread($fp, 1);
  $high = floor(ord($byte)/128); // check for has-more bit
  $bytestring .= $byte;
 }
 return decode_7bhm($bytestring); }
?>

When trying to read 32bit values (32 bit limitation depends on the word size of your machine) from a string that is represented in hex with the high bit set, 
eg. F9833234 
intval returns -1. The reason is the sign bit being set. This number is larger than can be saved in a signed int.
The way around this is to read the value in using two calls to intval.
eg. 
$val = intval(substr($str,0,4), 16); // read high 16 bit word
$val <<= 16; // shift hi word correct position
$val |= intval(substr($str, 4, 4), 16); // read low 16 bit word

If you just want to get the integer value of a number without all the hassle, just use intval()... like so:
$a1 = 10.4;
$a2 = -12.5;
$a3 = 44.1238503;
print intval($a1);  // returns 10
print intval($a2);  // returns -12
print intval($a3);  // returns 44
it's that easy!

I have found intval very useful for database security.
If you are passing a value via
- Data from user input
- Data that you have stored RAW on DB (witch is the best way) and you are using on a new sql statment
- Data from unknown/other origin
and the data is supposed to be an integer, I always run it through intval before I put it into the query (or you could use real_escape_string)
This prevents hackers from passing the variable as an SQL statement instead of a number in order to attack your database.

A function to get an integer from everywhere in a string (concatenated or not).
<?php
function str2int($string, $concat = true) {
  $length = strlen($string);  
  for ($i = 0, $int = '', $concat_flag = true; $i < $length; $i++) {
    if (is_numeric($string[$i]) && $concat_flag) {
      $int .= $string[$i];
    } elseif(!$concat && $concat_flag && strlen($int) > 0) {
      $concat_flag = false;
    }    
  }
  
  return (int) $int;
}
echo var_dump(str2int('sh12apen11')); // int(12)
echo var_dump(str2int('sh12apen11', false)); // int(1211)
echo var_dump(str2int('shap99en')); // int(99)
echo var_dump(intval('shap99en')); // int(0)
?>

Note:
$int = 0.99999999999999999;
echo intval($int); // returns 1
and
$int = 0.9999999999999999;
echo intval($int); // returns 0

intval used on bools returns either 1 or 0
I usually use this to properly set bools in my tables 
(assuming you use some kind of int like tinyints as booleans) : 
<?php 
$myvar = 'right value';
mysql_query('INSERT INTO mytable (activated) 
VALUES(' . intval($myvar === 'right value') . ')');
?>

Note that this function behaves different in PHP4/5 when parsing NAN-values. Try the following example:
<?php die( "Result = " . intval( NAN ) ); ?>
- In PHP 4 the result is 0
- In PHP 5 the result is 2^31 (running on 32bit)
Yhoko

Operating on integers gives puzzling results--which don't seem to have to do with the number of bits...
<?php
echo intval(1e10); // -1 on my system; 1410065408 in the example
echo intval(1e5); // 100000 (my own example: lower number--works all right)
echo intval(4e9); // -294967296 ! (my own example: somewhere in the middle)
echo intval(42000000); // 42000000 (as in the manual; reasonable)
echo intval(420000000000000000000); // -1 on my system at least. 0 in the example
// ...and yet still odder...
echo intval(4200000000); // -94967296! (my own example: somewhere in between)
?>

Say you have a string $s="3763328634" to be used as a key into the database, intval() this string will result in a different,smaller number (depends on the machine/OS). To keep the number intact but as an int/long type, do $s +=0; instead.

when converting some optional form values to positive integers and to be on the safe side, you can use this:
<?php $q=intval("0".$_REQUEST['q']); ?>

kris at mha dot ca:
Implicit typing. This is a feature, not a bug.
The == operator will convert your string to an int automatically (in this case) so that it is really comparing 123 and 123, which is of course the same.
If you use the === operator then this will not occur, as it will only match on the same value and type. This works as expected:
<?php
$tmp_array = "123,232,141";
if (intval($tmp_array) === $tmp_array)
{
  echo "'".intval($tmp_array)."' equals '$tmp_array'\n";
}
else
{
  echo "'".intval($tmp_array)."' does not equal '$tmp_array'\n";
}
?>

@kris:
If you had followed the following links:
"The common rules of integer casting apply." => http://us.php.net/manual/en/language.types.integer.php
"See String conversion to numbers" => http://us.php.net/manual/en/language.types.integer.php
Then you would have found the following: "The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used."
So this behaviour is a feature not a bug. 
The following code will work:
<?php
$tmp_array = str_replace(",", "", "123,232,141");
if(intval($tmp_array) == $tmp_array){
  echo intval($tmp_array) . " equals $tmp_array\n"; 
}else{
  echo intval($tmp_array) . " does not equal $tmp_array\n"; 
}
?>
Output:
123232141 equals 123232141

It seems that if you're trying to cast to integer (or use intval()) on integer of value bigger then 2147483646 it's hard to predict returned value.

intval() returns maxint on number_in_string, if the result would be bigger than it. But for float returns the signed 32 bit integer with the "same" value:
<?php
$num=-1000;
print($num."\n");
$i_str=sprintf("%u",$num);
print($i_str."\n");
$i1=intval($i_str);
print($i1."\n");
$i2=intval(floatval($i_str));
print($i2."\n");
?>
prints:
-1000
4294966296
2147483647
-1000

When retrieving numbers or integers from a MySQL DB, it's best to use intval(), or it will continue to be a string.
<?php
while($row = mysql_fetch_array($check)
{
 $_SESSION['id'] = inval($row['id']);
 $user_id = intval($_SESSION['id']); // Not sure if you need to do it again, but doesn't hurt.
}
is_int($_SESSION['id'])
is_int($user_id)
is_string($_SESSION['id'])
is_string($user_id)
// Output
true
true
false
false
?>

As a note using intval() as a check for string comparison will not work
$string="Pork";
$test=intval($string);
echo $test.'=='.$string;
if($string==$test)
  {
  echo '::Test PASS';  
  }else{
  echo '::Test FAIL';  
  }
if(is_numeric($string))
  {
  echo '::Test PASS';  
  }else{
  echo '::Test FAIL';  
  }
/*Produces 
0==Pork :: Test PASS
is_numeric(Pork) :: Test FAIL

i guess one of the important usage of intval is in links , because : 
imagine that u have a function that uses get method (for example an integer id ) to retrieve the data from DB , 
so for example if you get " id=58 " in your link and put that in u'r function that retrieves data from DB , that's fine , it works well
but what if some body put the " id=58djkdjsbvjkdsbvjkdbs " in the link ON PURPOSE !
in such situation and condition he will get an Database error 
because u'r function retrieves Data from DB 
so it good to be use intval in such situations
because if u use that u gonna be sure that what ever that passes from u'r DB related function is just a integer , No text and any strange character !
let me show u by example
$id = 12dfjgdfjgnd;
 
echo $id // output will be : 12dfjgdfjgnd
echo intval($id) // output will be : 12