Hướng dẫn dùng entier trong PHP

  • Định Nghĩa.
  • Cú pháp.
    • Cú pháp:
    • Trong đó.
    • Giá trị trả về.
  • Ví dụ.
    • code:
  • Ghi chú.
  • Hàm liên quan.
  • Thông tin thêm.

Định Nghĩa.

Hàm file_exists() sẽ kiểm tra xem file hoặc thư mục có tồn tại hay không.

Cú pháp.

Cú pháp:

file_exists ( string $filename ) : bool

Trong đó.

  • $filename là đường dẫn tới file hoặc thư mục cần kiểm tra.

– Lưu ý: Trên windows, sử dụng // computername / share / filename hoặc \\ computername \ share \ filename để kiểm tra các tệp trên mạng chia sẻ.

Giá trị trả về.

  • Hàm sẽ trả về True nếu file, thư mục truyền vào tồn tại. Ngược lại hàm sẽ trả về False..
Lưu ý: 
 - Hàm này sẽ trả về FALSE cho các liên kết tượng trưng trỏ đến các tệp không tồn tại.
 - Hàm này trả về FALSE cho các tệp không thể truy cập do hạn chế chế độ an toàn.
 Tuy nhiên, các tệp này vẫn có thể được bao gồm nếu chúng nằm trong safe_mode_include_dir.
 - Việc kiểm tra được thực hiện bằng cách sử dụng UID / GID thực thay vì kiểm tra có hiệu lực.
 - Vì loại số nguyên của PHP được ký và nhiều nền tảng sử dụng số nguyên 32 bit,
 một số hàm hệ thống tệp có thể trả về kết quả không mong muốn cho các tệp lớn hơn 2GB.

Ví dụ.

code:

Ghi chú.

  • Khi sử dụng SSL, Microsoft IIS sẽ vi phạm giao thức bằng cách đóng kết nối mà không gửi chỉ báo close_notify. PHP sẽ báo cáo đây là “SSL: Lỗi giao thức nghiêm trọng” khi bạn đến cuối dữ liệu. Để giải quyết vấn đề này, giá trị của error_Vporting nên được hạ xuống mức không bao gồm các cảnh báo. PHP có thể phát hiện phần mềm máy chủ IIS bị lỗi khi bạn mở luồng bằng cách sử dụng trình bao bọc https: // và sẽ chặn cảnh báo. Khi sử dụng fsockopen () để tạo ổ cắm ssl: //, nhà phát triển có trách nhiệm phát hiện và triệt tiêu cảnh báo này

Hàm liên quan.

  • readfile() – Đọc một file
  • fopen() – Mở một file hoặc một URL
  • fsockopen() – Mở kết nối ổ cắm Internet hoặc Unix
  • popen() – Opens process file pointer
  • file_get_contents() – Reads entire file into a string
  • include – include
  • stream_context_create() – Creates a stream context

Thông tin thêm.

  • Lưu ý: Kết quả của chức năng này được lưu trữ. Xem Clearstatcache () để biết thêm chi tiết. Đó là một lưu ý khá lớn. Đừng quên điều này, vì nó có thể khiến file_exists () của bạn hoạt động bất ngờ – có thể tại thời điểm sản xuất;)
  • Tôi cần đo lường hiệu suất cho một dự án, vì vậy tôi đã thực hiện một thử nghiệm đơn giản với một triệu kiểm tra file_exists () và is_file (). Trong một kịch bản, chỉ có bảy trong số các tệp tồn tại. Trong lần thứ hai, tất cả các tập tin tồn tại. is_file () cần 3.0 cho kịch bản một và 3,3 giây cho kịch bản hai. file_exists () cần lần lượt 2,8 và 2,9 giây. Các số tuyệt đối phụ thuộc vào khóa học, nhưng nó chỉ ra rõ ràng rằng file_exists () nhanh hơn.
  • Lưu ý rằng realpath () sẽ trả về false nếu tệp không tồn tại. Vì vậy, nếu bạn định tuyệt đối hóa đường dẫn và giải quyết các liên kết tượng trưng, ​​bạn chỉ cần kiểm tra giá trị trả về từ realpath () thay vì gọi file_exists () trước

Các bạn có thể xem chi tiết hơn trên php.net.

Hi vọng với bài viết này, bạn đã hiểu rõ ứng dụng của hàm file_exists() trong PHP. Nếu bạn thấy bài viết hay và có ý nghĩa hãy like và chia sẻ bài viết này để mọi người cùng nhau học tập nhé.
Cảm ơn các bạn đã ghé thăm codetutam.com

An int is a number of the set ℤ = {..., -2, -1, 0, 1, 2, ...}.

See also:

  • Arbitrary length integer / GMP
  • Floating point numbers
  • Arbitrary precision / BCMath

Syntax

ints can be specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation. The negation operator can be used to denote a negative int.

To use octal notation, precede the number with a 0 (zero). As of PHP 8.1.0, octal notation can also be preceded with 0o or 0O. To use hexadecimal notation precede the number with 0x. To use binary notation precede the number with 0b.

As of PHP 7.4.0, integer literals may contain underscores (_) between digits, for better readability of literals. These underscores are removed by PHP's scanner.

Example #1 Integer literals

$a 1234// decimal number
$a 0123// octal number (equivalent to 83 decimal)
$a 0o123// octal number (as of PHP 8.1.0)
$a 0x1A// hexadecimal number (equivalent to 26 decimal)
$a 0b11111111// binary number (equivalent to 255 decimal)
$a 1_234_567// decimal number (as of PHP 7.4.0)
?>

Formally, the structure for int literals is as of PHP 7.4.0 (previously, underscores have not been allowed):

decimal     : [1-9][0-9]*(_[0-9]+)*
            | 0

hexadecimal : 0[xX][0-9a-fA-F]+(_[0-9a-fA-F]+)*

octal       : 0[oO]?[0-7]+(_[0-7]+)*

binary      : 0[bB][01]+(_[01]+)*

integer     : decimal
            | hexadecimal
            | octal
            | binary

The size of an int is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). 64-bit platforms usually have a maximum value of about 9E18. PHP does not support unsigned ints. int size can be determined using the constant PHP_INT_SIZE, maximum value using the constant PHP_INT_MAX, and minimum value using the constant PHP_INT_MIN.

Integer overflow

If PHP encounters a number beyond the bounds of the int type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the int type will return a float instead.

Example #2 Integer overflow on a 32-bit system

$large_number 2147483647;
var_dump($large_number);                     // int(2147483647)$large_number 2147483648;
var_dump($large_number);                     // float(2147483648)$million 1000000;
$large_number =  50000 $million;
var_dump($large_number);                     // float(50000000000)
?>

Example #3 Integer overflow on a 64-bit system

$large_number 9223372036854775807;
var_dump($large_number);                     // int(9223372036854775807)$large_number 9223372036854775808;
var_dump($large_number);                     // float(9.2233720368548E+18)$million 1000000;
$large_number =  50000000000000 $million;
var_dump($large_number);                     // float(5.0E+19)
?>

There is no int division operator in PHP, to achieve this use the intdiv() function. 1/2 yields the float 0.5. The value can be cast to an int to round it towards zero, or the round() function provides finer control over rounding.

var_dump(25/7);         // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7));  // float(4)
?>

Converting to integer

To explicitly convert a value to int, use either the (int) or (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an int argument. A value can also be converted to int with the intval() function.

If a resource is converted to an int, then the result will be the unique resource number assigned to the resource by PHP at runtime.

See also Type Juggling.

From booleans

false will yield 0 (zero), and true will yield 1 (one).

From floating point numbers

When converting from float to int, the number will be rounded towards zero. As of PHP 8.1.0, a deprecation notice is emitted when implicitly converting a non-integral float to int which loses precision.

function foo($value): int {
  return 
$value
}
var_dump(foo(8.1)); // "Deprecated: Implicit conversion from float 8.1 to int loses precision" as of PHP 8.1.0
var_dump(foo(8.1)); // 8 prior to PHP 8.1.0
var_dump(foo(8.0)); // 8 in both casesvar_dump((int)8.1); // 8 in both cases
var_dump(intval(8.1)); // 8 in both cases
?>

If the float is beyond the boundaries of int (usually +/- 2.15e+9 = 2^31 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms), the result is undefined, since the float doesn't have enough precision to give an exact int result. No warning, not even a notice will be issued when this happens!

Note:

NaN and Infinity will always be zero when cast to int.

Warning

Never cast an unknown fraction to int, as this can sometimes lead to unexpected results.

echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>

See also the warning about float precision.

From strings

If the string is numeric or leading numeric then it will resolve to the corresponding integer value, otherwise it is converted to zero (0).

From NULL

null is always converted to zero (0).

From other types

Caution

The behaviour of converting to int is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.

php at richardneill dot org

9 years ago

A leading zero in a numeric literal means "this is octal". But don't be confused: a leading zero in a string does not. Thus:
$x = 0123;          // 83
$y = "0123" + 0     // 123

d_n at NOSPAM dot Loryx dot com

15 years ago

Here are some tricks to convert from a "dotted" IP address to a LONG int, and backwards. This is very useful because accessing an IP addy in a database table is very much faster if it's stored as a BIGINT rather than in characters.

IP to BIGINT:
  $ipArr    = explode('.',$_SERVER['REMOTE_ADDR']);
 
$ip       = $ipArr[0] * 0x1000000
           
+ $ipArr[1] * 0x10000
           
+ $ipArr[2] * 0x100
           
+ $ipArr[3]
            ;
?>

IP as BIGINT read from db back to dotted form:

Keep in mind, PHP integer operators are INTEGER -- not long. Also, since there is no integer divide in PHP, we save a couple of S-L-O-W floor ()'s by doing bitshifts. We must use floor(/) for $ipArr[0] because though $ipVal is stored as a long value, $ipVal >> 24 will operate on a truncated, integer value of $ipVal! $ipVint is, however, a nice integer, so
we can enjoy the bitshifts.

        $ipVal = $row['client_IP'];
       
$ipArr = array(0 =>
                   
floor$ipVal               / 0x1000000) );
       
$ipVint   = $ipVal-($ipArr[0]*0x1000000); // for clarity
       
$ipArr[1] = ($ipVint & 0xFF0000)  >> 16;
       
$ipArr[2] = ($ipVint & 0xFF00  )  >> 8;
       
$ipArr[3] =  $ipVint & 0xFF;
       
$ipDotted = implode('.', $ipArr);
?>

dhairya lakhera

4 years ago

-------------------------------------------------------------------------
Question :
var_dump((int) 010);  //Output 8

var_dump((int) "010"); //output 10

First one is octal notation so the output is correct. But what about the when converting "010" to integer. it should be also output 8 ?
--------------------------------------------------------------------------
Answer :

Casting to an integer using (int) will always cast to the default base, which is 10.

Casting a string to a number this way does not take into account the many ways of formatting an integer value in PHP (leading zero for base 8, leading "0x" for base 16, leading "0b" for base 2). It will simply look at the first characters in a string and convert them to a base 10 integer. Leading zeroes will be stripped off because they have no meaning in numerical values, so you will end up with the decimal value 10 for (int)"010".

Converting an integer value between bases using (int)010 will take into account the various ways of formatting an integer. A leading zero like in 010 means the number is in octal notation, using (int)010 will convert it to the decimal value 8 in base 10.

This is similar to how you use 0x10 to write in hexadecimal (base 16) notation. Using (int)0x10 will convert that to the base 10 decimal value 16, whereas using (int)"0x10" will end up with the decimal value 0: since the "x" is not a numerical value, anything after that will be ignored.

If you want to interpret the string "010" as an octal value, you need to instruct PHP to do so. intval("010", 8) will interpret the number in base 8 instead of the default base 10, and you will end up with the decimal value 8. You could also use octdec("010") to convert the octal string to the decimal value 8. Another option is to use base_convert("010", 8, 10) to explicitly convert the number "010" from base 8 to base 10, however this function will return the string "8" instead of the integer 8.

Casting a string to an integer follows the same the logic used by the intval function:

Returns the integer value of var, using the specified base for the conversion (the default is base 10).
intval allows specifying a different base as the second argument, whereas a straight cast operation does not, so using (int) will always treat a string as being in base 10.

php > var_export((int) "010");
10
php > var_export(intval("010"));
10
php > var_export(intval("010", 8));
8

egwayjen at gmail dot com

4 years ago

"There is no integer division operator in PHP". But since PHP 7, there is the intdiv function.

ganlvtech at qq dot com

2 years ago

Be aware of float to int cast overflow

// You may expected these
var_dump(0x7fffffffffffffff);                // int(9223372036854775807)
var_dump(0x7fffffffffffffff + 1);            // float(9.2233720368548E+18)
var_dump((int)(0x7fffffffffffffff + 1));     // int(9223372036854775807)
var_dump(0x7fffffffffffffff + 1 > 0);        // bool(true)
var_dump((int)(0x7fffffffffffffff + 1) > 0); // bool(true)
var_dump((int)'9223372036854775807');        // int(9223372036854775807)
var_dump(9223372036854775808);               // float(9.2233720368548E+18)
var_dump((int)'9223372036854775808');        // int(9223372036854775807)
var_dump((int)9223372036854775808);          // int(9223372036854775807)

// But actually, it likes these

var_dump(0x7fffffffffffffff);                // int(9223372036854775807)
var_dump(0x7fffffffffffffff + 1);            // float(9.2233720368548E+18)
var_dump((int)(0x7fffffffffffffff + 1));     // int(-9223372036854775808)   <-----
var_dump(0x7fffffffffffffff + 1 > 0);        // bool(true)
var_dump((int)(0x7fffffffffffffff + 1) > 0); // bool(false)                 <-----
var_dump((int)'9223372036854775807');        // int(9223372036854775807)
var_dump(9223372036854775808);               // float(9.2233720368548E+18)
var_dump((int)'9223372036854775808');        // int(9223372036854775807)
var_dump((int)9223372036854775808);          // int(-9223372036854775808)   <-----?>

These overflows are dangerous when you try to compare it with zero, or substract it from another value (e.g. money).

[email protected]

15 years ago

Be careful with using the modulo operation on big numbers, it will cast a float argument to an int and may return wrong results. For example:
    $i = 6887129852;
    echo
"i=$i\n";
    echo
"i%36=".($i%36)."\n";
    echo
"alternative i%36=".($i-floor($i/36)*36)."\n";
?>
Will output:
i=6.88713E+009
i%36=-24
alternative i%36=20

Anonymous

7 years ago

Converting to an integer works only if the input begins with a number
(int) "5txt" // will output the integer 5
(int) "before5txt" // will output the integer 0
(int) "53txt" // will output the integer 53
(int) "53txt534text" // will output the integer 53

litbai

6 years ago

$ipArr = explode('.', $ipString);
$ipVal = ($ipArr[0] << 24)
       + (
$ipArr[1] << 16)
       + (
$ipArr[2] << 8)
       +
$ipArr[3]
        ;
?>
1. the priority of bit op is lower than '+',so there should be brackets.
2. there is no unsighed int in PHP, if you use 32 bit version,the code above will get negative result when the first position of IP string greater than 127.
3. what the code actually do is calculate the integer value of transformed 32 binary bit from IP string.

Anonymous

15 years ago

To force the correct usage of 32-bit unsigned integer in some functions, just add '+0'  just before processing them.

for example
echo(dechex("2724838310"));
will print '7FFFFFFF'
but it should print 'A269BBA6'

When adding '+0' php will handle the 32bit unsigned integer
correctly
echo(dechex("2724838310"+0));
will print 'A269BBA6'

Anonymous

18 years ago

Sometimes you need to parse an unsigned
32 bit integer. Here's a function I 've used:

                                                                                    function parse_unsigned_int($string) {
        $x = (float)$string;
        if ($x > (float)2147483647)
            $x -= (float)"4294967296";
        return (int)$x;
    }

darkshire

14 years ago

d_n at NOSPAM dot Loryx dot com
13-Aug-2007 05:33
Here are some tricks to convert from a "dotted" IP address to a LONG int, and backwards. This is very useful because accessing an IP addy in a database table is very much faster if it's stored as a BIGINT rather than in characters.

IP to BIGINT:
  $ipArr    = explode('.',$_SERVER['REMOTE_ADDR']);
 
$ip       = $ipArr[0] * 0x1000000
           
+ $ipArr[1] * 0x10000
           
+ $ipArr[2] * 0x100
           
+ $ipArr[3]
            ;
?>

This can be written in a bit more efficient way:
  $ipArr    = explode('.',$_SERVER['REMOTE_ADDR']);
 
$ip       = $ipArr[0]<<24
           
+ $ipArr[1]<<16
           
+ $ipArr[2] <<8
           
+ $ipArr[3]
            ;
?>

shift is more cheaper.

kuzawinski dot marcin_NOSPAM at gmail dot com

2 years ago

Integer literals may be decimal, octal, hexadecimal or binary, but integer values have single representation;

var_dump

(010); // int(8) NOT int(010)
var_dump(0x10); // int(16) NOT int(0x10)
var_dump(0b10); // int(2) NOT int(0b10) ?>

This is the reason why casting integer to string gives us always a decimal:

var_dump

((string) 010); // string(8) NOT string(010)
var_dump((string) 0x10); // string(16) NOT string(0x10)
var_dump((string) 0b10); // string(2) NOT string(0b10)?>

Jacek

15 years ago

On 64 bits machines max integer value is 0x7fffffffffffffff (9 223 372 036 854 775 807).

eric

14 years ago

In response to the comment by me at troyswanson dot net:

-2147483648 falls into the range of 32 bit signed integers yet php treats it as a float.  However, -2147483647-1 is treated as an integer.

The following code demonstrates:
    var_dump(-2147483648); //float(-2147483648)
   
var_dump(-2147483647 - 1); //int(-2147483648)
?>

This is probably very similar to the MS C bug which also treats -2147483648 as an UNSIGNED because it thinks it's out of the range of a signed int.

The problem is that the parser does not view "-x" as a single token, but rather as two, "-" and "x".  Since "x" is out of the range of an INT, it is promoted to float, even though in this unique case, "-x" is in the range of an int.

The best cure is probably to replace "-2147483648" with "0x80000000", as that is the hexadecimal equivalent of the same number.

Hope that helps explain what's going on

Peace

- Eric / fez

pere dot cil at wanadoo dot fr

11 years ago

Please also note that the maximum stored in the integer depends on the platform / compilation; on windows xp 32 bits, the following value:

0x5468792130ABCDEF

echoes to:

6.0822444802213E+18 (cast to float)

On a fully 64 bits system, it echoes to:

6082244480221302255

wbcarts at juno dot com

13 years ago

PHP offers a slew of built-in functions and automatic type-casting routines which can get pretty complicated. But most of the time, you still have to take matters into your own hands and allow PHP to do its thing. In that case, and something that has NOT been mentioned, is how to construct your code. To keep things simple, I divide all my scripts in half. The top half gives my scripts the "capability" they need, and the lower half is the actual code to be "run" or "executed".

/*
* build the program's capability - define variables and functions...
*/
$item_label = '';        // type string
$item_price = 0.0;       // type float
$item_qty = 1;           // type integer
$item_total = 0.0;       // type float - to set use calculate()function calculate(){
  global
$item_price, $item_qty, $item_total;
 
$item_price = number_format($item_price, 2);
 
$item_total = number_format(($item_price * $item_qty), 2);
}

function

itemToString() {
  global
$item_label, $item_price, $item_qty, $item_total;
  return
"$item_label [price=\$$item_price, qty=$item_qty, total=\$$item_total]";
}
/*
* run the program - set data, call methods...
*/
$item_label = "Coffee";
$item_price = 3.89;
$item_qty = 2;
calculate();           // set $item_total
echo itemToString();   // -> Coffee [price=$3.89, qty=2, total=$7.78]$item_label = "Chicken";
$item_price = .80;     // per lb.
$item_qty = 3.5;       // lbs.
calculate();           // set $item_total
echo itemToString();   // -> Chicken [price=$0.80, qty=3.5, total=$2.80]
?>
Note: All type-casting is done by PHP's built-in number_format() method. This allows our program to enter any number (float or int) on item price or quantity in the runtime part of our script. Also, if we explicitly cast values to integer in the capability part of our script, then we start getting results that may not be desirable for this program. For example, if in the calculate method we cast item_qty to integer, then we can no longer sell chicken by the pound!

13453814063 at 163 dot com

4 years ago

$e = 0x8000000000000000;
$e2 = 0b1000000000000000000000000000000000000000000000000000000000000000;
if ($e == $e2){
    echo "e==e2
";
}else{
    echo "e!=e2
";
}
pirnt "e!=e2"
----------------------------
echo decbin($e) . "
";
echo decbin($e2) . "
";
the result is :
1000000000000000000000000000000000000000000000000000000000000000
111111111111111111111111111111111111111111111111111110000000000

dewi at dewimorgan dot com

7 years ago

Note that the soft-typing of numbers in PHP means that some things become very difficult. For example, efficiently emulating the more common linear congruential generators (LCGs) for fast, deterministic, pseudo-randomness. The naive code to create the next value in a sequence (for power-of-2 values of $m) is:

$seed = ($seed * $a + $c) % $m;

...where $m, $a, and $c are values and data types carefully chosen such that repeating this operation will eventually generate every value in the range $0 to $m, with no repetition.

I can find no good commonly used LCGs which use PHP-compatible values. The LCG values used in by rand() in systems like Borland Delphi, Virtual Pascal, MS Visual/Quick C/C++, VMS's MTH$RANDOM, old versions of glibc, Numerical Recipes, glibc, GCC, ANSI C, Watcom, Digital Mars, CodeWarrior, IBM VisualAge C/C++, java.util.Random, Newlib, MMX... *all* fail when ported, for one of two reasons, and sometimes both:

- In PHP on 32 bit machines and all Windows machines, $m = 2^32 or larger requires UInt or even UInt64, or the result becomes negative.

- Large $a multiplied by an integer seed gets converted to a float64, but the number can be too long for the 53-bit mantissa, and it drops the least significant digits... but the LCG code above requires that the most significant digits should be lost.

These are two classes of problem to beware of when porting integer math to PHP,  and I see no clean and efficient way to avoid either one.

So if designing a cross-platform system that must work in PHP, you must select LCG values that fit the following criteria:
$m = 2^31 or less (PHP limitation). Recommend: 2^31.
$a = Less than 2^22 (PHP limitation); $a-1 divisible by all prime factors of $m; $a-1 divisible by 4 if $m is. Recommend: 1+(4*(any prime <= 1048573)).
$c = smaller than (2^53-($m*$a)) (PHP limitation); relatively prime with $m. Recommend: any prime <= 23622320123.

jmw254 at cornell dot edu

16 years ago

Try this one instead:

function iplongtostring($ip)
{
    $ip=floatval($ip); // otherwise it is capped at 127.255.255.255

    $a=($ip>>24)&255;
    $b=($ip>>16)&255;
    $c=($ip>>8)&255;
    $d=$ip&255;

    return "$a.$b.$c.$d";
}