How do I convert a string to a number in PHP?

问题

I want to convert these types of values, '3', '2.34', '0.234343', etc. to a number. In JavaScript we can use Number(), but is there any similar method available in PHP?

Input             Output
'2'               2
'2.34'            2.34
'0.3454545'       0.3454545

回答1:

You don't typically need to do this, since PHP will coerce the type for you in most circumstances. For situations where you do want to explicitly convert the type, cast it:

$num = "3.14";
$int = (int)$num;
$float = (float)$num;

回答2:

There are a few ways to do so:

Cast the strings to numeric primitive data types:

$num = (int) "10";
$num = (double) "10.12"; // same as (float) "10.12";

Perform math operations on the strings:
```
$num = "10" + 1;
$num = floor("10.1");
```

Use intval() or floatval():

$num = intval("10");
$num = floatval("10.1");

Use settype().

回答3:

In whatever (loosely-typed) language you can always cast a string to a number by adding a zero to it.

However, there is very little sense in this as PHP will do it automatically at the time of using this variable, and it will be cast to a string anyway at the time of output.

Note that you may wish to keep dotted numbers as strings, because after casting to float it may be changed unpredictably, due to float numbers' nature.

回答4:

To avoid problems try intval($var). Some examples:

<?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 (octal as starts with zero)
echo intval('042');                   // 42
echo intval(1e10);                    // 1410065408
echo intval('1e10');                  // 1
echo intval(0x1A);                    // 26 (hex as starts with 0x)
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
?>

回答5:

You can use:

(int)(your value);

Or you can use:

intval(string)

回答6:

If you want get a float for $value = '0.4', but int for $value = '4', you can write:

$number = ($value == (int) $value) ? (int) $value : (float) $value;

It is little bit dirty, but it works.

回答7:

You can always add zero to it!

Input             Output
'2' + 0           2 (int)
'2.34' + 0        2.34 (float)
'0.3454545' + 0   0.3454545 (float)

回答8:

Instead of having to choose whether to convert the string to int or float, you can simply add a 0 to it, and PHP will automatically convert the result to a numeric type.

// Being sure the string is actually a number
if (is_numeric($string))
    $number = $string + 0;
else // Let the number be 0 if the string is not a number
    $number = 0;

回答9:

In PHP you can use intval(string) or floatval(string) functions to convert strings to numbers.

回答10:

Yes, there is a similar method in PHP, but it is so little known that you will rarely hear about it. It is an arithmetic operator called "identity", as described here:

Aritmetic Operators

To convert a numeric string to a number, do as follows:

$a = +$a;

回答11:

Just a little note to the answers that can be useful and safer in some cases. You may want to check if the string actually contains a valid numeric value first and only then convert it to a numeric type (for example if you have to manipulate data coming from a db that converts ints to strings). You can use is_numeric() and then floatval():

$a = "whatever"; // any variable

if (is_numeric($a)) 
    var_dump(floatval($a)); // type is float
else 
    var_dump($a); // any type

回答12:

Here is the function that achieves what you are looking for. First we check if the value can be understood as a number, if so we turn it into an int and a float. If the int and float are the same (e.g., 5 == 5.0) then we return the int value. If the int and float are not the same (e.g., 5 != 5.3) then we assume you need the precision of the float and return that value. If the value isn't numeric we throw a warning and return null.

function toNumber($val) {
    if (is_numeric($val)) {
        $int = (int)$val;
        $float = (float)$val;

        $val = ($int == $float) ? $int : $float;
        return $val;
    } else {
        trigger_error("Cannot cast $val to a number", E_USER_WARNING);
        return null;
    }
}

回答13:

I've found that in JavaScript a simple way to convert a string to a number is to multiply it by 1. It resolves the concatenation problem, because the "+" symbol has multiple uses in JavaScript, while the "*" symbol is purely for mathematical multiplication.

Based on what I've seen here regarding PHP automatically being willing to interpret a digit-containing string as a number (and the comments about adding, since in PHP the "+" is purely for mathematical addition), this multiply trick works just fine for PHP, also.

I have tested it, and it does work... Although depending on how you acquired the string, you might want to apply the trim() function to it, before multiplying by 1.

回答14:

Here is a function I wrote to simplify things for myself:

It also returns shorthand versions of boolean, integer, double and real.

function type($mixed, $parseNumeric = false)
{        
    if ($parseNumeric && is_numeric($mixed)) {
        //Set type to relevant numeric format
        $mixed += 0;
    }
    $t = gettype($mixed);
    switch($t) {
        case 'boolean': return 'bool'; //shorthand
        case 'integer': return 'int';  //shorthand
        case 'double': case 'real': return 'float'; //equivalent for all intents and purposes
        default: return $t;
    }
}

Calling type with parseNumeric set to true will convert numeric strings before checking type.

Thus:

type("5", true) will return int

type("3.7", true) will return float

type("500") will return string

Just be careful since this is a kind of false checking method and your actual variable will still be a string. You will need to convert the actual variable to the correct type if needed. I just needed it to check if the database should load an item id or alias, thus not having any unexpected effects since it will be parsed as string at run time anyway.

Edit

If you would like to detect if objects are functions add this case to the switch:

case 'object': return is_callable($mixed)?'function':'object';

回答15:

In addition to Boykodev's answer I suggest this:

Input             Output
'2' * 1           2 (int)
'2.34' * 1        2.34 (float)
'0.3454545' * 1   0.3454545 (float)

回答16:

$a = "10";

$b = (int)$a;

You can use this to convert a string to an int in PHP.

回答17:

Simply you can write like this:

<?php
    $data = ["1","2","3","4","5"];
    echo json_encode($data, JSON_NUMERIC_CHECK);
?>

回答18:

You can use:

((int) $var)   ( but in big number it return 2147483647 :-) )

But the best solution is to use:

if (is_numeric($var))
    $var = (isset($var)) ? $var : 0;
else
    $var = 0;

if (is_numeric($var))
    $var = (trim($var) == '') ? 0 : $var;
else
    $var = 0;

回答19:

You can change the data type as follows

$number = "1.234";

echo gettype ($number) . "\n"; //Returns string

settype($number , "float");

echo gettype ($number) . "\n"; //Returns float

For historical reasons "double" is returned in case of a float.

PHP Documentation

回答20:

All suggestions lose the numeric type.

This seems to me a best practice:

function str2num($s){
// Returns a num or FALSE
    $return_value =  !is_numeric($s) ? false :               (intval($s)==floatval($s)) ? intval($s) :floatval($s);
    print "\nret=$return_value type=".gettype($return_value)."\n";
}

回答21:

Only multiply the number by 1 so that the string is converted to type number.

//String value
$string = "5.1"
if(is_numeric($string)){
  $numeric_string = $string*1;
}

回答22:

PHP will do it for you within limits

<?php
   $str = "3.148";
   $num = $str;

   printf("%f\n", $num);
?>

回答23:

There is a way:

$value = json_decode(json_encode($value, JSON_NUMERIC_CHECK|JSON_PRESERVE_ZERO_FRACTION|JSON_UNESCAPED_SLASHES), true);

Using is_* won't work, since the variable is a: string.

Using the combination of json_encode() and then json_decode() it's converted to it's "true" form. If it's a true string then it would output wrong.

$num = "Me";
$int = (int)$num;
$float = (float)$num;

var_dump($num, $int, $float);

Will output: string(2) "Me" int(0) float(0)

回答24:

I got the question "say you were writing the built in function for casting an integer to a string in PHP, how would you write that function" in a programming interview. Here's a solution.

$nums = ["0","1","2","3","4","5","6","7","8","9"];
$int = 15939; 
$string = ""; 
while ($int) { 
    $string .= $nums[$int % 10]; 
    $int = (int)($int / 10); 
} 
$result = strrev($string);

回答25:

I've been reading through answers and didn't see anybody mention the biggest caveat in PHP's number conversion.

The most upvoted answer suggests doing the following:

$str = "3.14"
$intstr = (int)$str // now it's a number equal to 3

That's brilliant. PHP does direct casting. But what if we did the following?

$str = "3.14is_trash"
$intstr = (int)$str

Does PHP consider such conversions valid?

Apparently yes.

PHP reads the string until it finds first non-numerical character for the required type. Meaning that for integers, numerical characters are [0-9]. As a result, it reads 3, since it's in [0-9] character range, it continues reading. Reads . and stops there since it's not in [0-9] range.

Same would happen if you were to cast to float or double. PHP would read 3, then ., then 1, then 4, and would stop at i since it's not valid float numeric character.

As a result, "million" >= 1000000 evaluates to false, but "1000000million" >= 1000000 evaluates to true.

回答26:

Different approach:

Push it all into an array / associative array.
json_encode($your_array, JSON_NUMERIC_CHECK); optionally decode it back
?
Profit!

来源：https://stackoverflow.com/questions/8529656/how-do-i-convert-a-string-to-a-number-in-php

标签

php

casting

type-conversion