type conversion in php

In the process of PHP development, we will definitely encounter that the received data type is different from the data type we want. In this case, we can use PHP has type conversion. Today we are going to talk about type conversion in PHP. Without further ado, let’s take a look!

Convert to integers and floating point numbers

The types that can be converted to integers only include floating point numbers, Boolean values, strings and resources. Arrays and objects cannot be converted to numeric types.

When converting to floating point numbers, except that there is its own set of rules for converting strings to floating point numbers, other values ​​​​are first converted to integers (under the premise that they can be converted to integers), and then converted is a floating point number.

When converting from a floating point number to an integer, it is rounded down (the decimal part is discarded). If the floating point number is outside the integer range, the result is undefined because there is insufficient precision to give an exact integer result. There is no warning in this case, not even any notification!

Since PHP 7.0.0, NaN and Infinity are no longer undefined or platform-dependent when converted to integer, but will become zero.

When a string (only supports decimal) is converted to an integer, legal integer characters are searched starting from the first character until the end of the string or a non-integer character is encountered, and the found characters are converted into integers. If none Legal characters, the result is 0.

When converting a string to a floating-point number, search for legal floating-point characters starting from the first character until the end of the string or encountering a non-floating-point character. Convert the found character to a floating-point number. If there is no legal character, character, the result is 0.

If the string does not contain '.', 'e' or 'E' and its numeric value is within the range of integers (defined by PHP_INT_MAX), the string will be treated as an integer. value. In all other cases the value is treated as float.

The beginning of the string determines its value. If the string begins with a legal numeric value, that numeric value is used. Otherwise its value is 0 (zero). Legal values ​​consist of an optional sign, followed by one or more digits (possibly with a decimal point), and then an optional exponent part. The exponent part consists of 'e' or 'E' followed by one or more digits.

echo 0+"0xff","\n";   // 0  
echo 0+"2.33","\n";   // 2.33  
echo 0+"033","\n";    // 33  
echo 0+"2e3","\n";    // 2000

null -> 0
true -> 1
false -> 0

When converting resource to integer, the result will be the unique resource number assigned to resource by PHP runtime.

Convert to string

true -> "1"
false -> ""
null -> ""

Convert integer or floating point number to string, directly represent the value into string (decimal, decimal point form )

When the array is converted to a string, the result is "Array"

When the object is converted to a string, the result is "Object"

When the resource is converted to a string , a string like "Resource id#1"

is converted into a Boolean value

When other values ​​are converted to Boolean values, only the following values ​​will be converted to false, and all others will be converted to true:

Integer 0

Floating point number 0.0

String "0"

String""

Empty array (no elements)

Empty object (no members)

NULL (including not set yet) Variables)

SimpleXML object generated from empty tags

Convert to array

When integers, floating point numbers, Boolean values, and strings are converted into arrays, a new array is obtained. The array has only one element, so the value of the element is the corresponding integer, floating point number, Boolean value, or string.

When converting null to an array, the result is an empty array:

echo var_dump((array)null);  
//array(0) {

}

Show conversion

1. You can Add a cast operator in front of the variable:

(int)(integer)
(float)(double)(real)
(bool)(boolean)
(string)
(array)
(object)

This method does not change the data type of the variable, but only changes the data type of the expression.

2. Use the settype(var, type) function

$var = true;  
settype($var, "integer");  
var_dump($var);  // int(1)

It can be seen that the type and value of the variable have been modified

3. Use intval()/floatval() /boolval()/strval() series functions

Note that these functions do not modify the value of the variable

$var = "0xff";  
$num = intval($var, 16);  
var_dump($var);  // string(4) "0xff"  
var_dump($num);  // int(255)

If the first parameter of the intval() function is a string, then An optional second parameter can be provided to specify the base of the value in the string. If this parameter is not provided, it will be processed in decimal by default. If the parameter is specified as 0, it will be automatically determined in the form of a string (starting with 0x is hexadecimal...)

intval() cannot be used Object type

This function returns a converted integer value. If the conversion fails, it returns 0. If the parameter is an array, a non-empty array returns 1, and an empty array returns 0

boolval() Gets the Boolean value of the parameter.

floatval()The parameters of the function can only be scalar types, such as integers, floating point numbers, Boolean values, and strings. Cannot be used with arrays or objects.

The parameters of the strval() function can only be scalar types, such as integers, floating point numbers, Boolean values, and strings. Cannot be used with arrays or objects.

Under what circumstances will no implicit conversion be performed?

#Both operands of arithmetic operator will be converted Is a numeric type.

The two operands of the string concatenation operator will be converted to string type.

In an expression that requires a string, it will be automatically converted to string. This conversion occurs, for example, when using the functions echo or print, or when comparing a variable to a string.

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