PHP learning data type automatic conversion

In development, PHP, as a dynamically typed language, has very high flexibility for variable data types. Therefore, there is no need to specify the data type when writing, but its type is determined based on assignment at runtime. This provides programmers with great convenience, but sometimes it can also lead to some problems, such as improper type conversion. PHP provides many type conversion functions and some type judgment functions. This article will introduce some common methods and problems of PHP type conversion.

1. Strong type and weak type

PHP variables have two types: strong type and weak type. Strong typing means that the type of a variable is relatively fixed and cannot be changed at will once it is defined. For example, in Java, if you define an integer variable, you can only pass integer data to it. Any other type of data will cause a compilation error. Weak typing means that the type of the variable is not fixed and can be changed dynamically. For example, in PHP, you can define a variable of type string and directly assign an integer variable to it at runtime.

2. Forced type conversion

PHP provides some functions to implement forced type conversion. The naming rules of these functions all start with "(the type that needs to be converted to)" (Variable that needs to be converted)" is named in the form, such as (int)$var, $str, (float)$var, etc. Below we introduce some commonly used cast conversion functions.

a. (bool) or (boolean)

(boolean)$var or (bool)$var can convert a variable to Boolean type. Among them, for a non-Boolean value, it will be converted into a Boolean value. The conversion rules are as follows:

• 0, 0.0, "", "0", "false", " null" will be converted into Boolean false.
• Other values ​​will be converted into Boolean true.

b. (int) or (integer)

(integer)$var or (int)$var can convert a variable into an integer. For a non-integer value, it will be converted to an integer as much as possible. The conversion rules are as follows:

• Floating point numbers will be forced to be converted to integers, and the integer part will be truncated.
• Strings will be converted to integers. If the string does not start with a number, it will be converted to 0.
• The Boolean value true will be converted to 1, and false will be converted to 0.
• Arrays and objects cannot be converted to integers, they will be converted to 1.

c. (float) or (double)

(double)$var or (float)$var can convert a variable into a floating point type. For a non-floating point value, it will be converted to a floating point type as much as possible. The conversion rules are as follows:

• If it is an integer type, it will be converted directly to a floating point type.
• If it is a string, it will be converted to a floating point number. If the string does not start with a number, it will be converted to 0.
• The Boolean value true will be converted to 1.0, and false will be converted to 0.0.
• Arrays and objects cannot be converted to floating point numbers, they will be converted to 1.0.

d. (string)

(string)$var can convert a variable into a string. The conversion rules are as follows:

• If it is a numerical value type, it is converted directly to a string.
• If it is a Boolean type, the Boolean value true will be converted into the string "1", and false will be converted into the empty string "".
• If it is an array, it will be converted to the string "Array".
• If it is an object, it will be converted to the string "Object".
• null will be converted to the empty string "".

e. (array)

(array)$var can convert a variable into an array. $var must be an object or a comma-separated string. The conversion rules are as follows:

• The object will be converted into an array containing the object's properties and methods. The
• delimited string will be converted into a numerically indexed array, each element is a non-null value separated by the delimiter.

f. (object)

(object)$var can convert a variable into an object. $var must be an array or an object. If $var is an array, it will be converted to an empty standard object (stdClass).

3. Automatic type conversion

As a dynamic type language, PHP automatically determines and converts variable types. Let's take a look at some rules for automatic type conversion.

a. Adding integers and floating point types

In PHP, when adding integers and floating point types, the integers will be automatically converted to floating point types and then added. add.

b. Adding strings and numeric types

In PHP, when adding strings and numeric types, the strings will be converted into numeric types and then added.

c. Array and Object Conversion

When converting an array or object to another type, they are converted to an empty standard array or standard object.

d. Adding Boolean and numeric types to strings

In PHP, when adding Boolean and numeric types to strings, they will be converted to string types, and then Add them up again.

4. Type detection

PHP provides some type detection functions that can be used to determine the type of a variable. Below we introduce some commonly used type detection functions.

a. is_bool()

is_bool($var) is used to determine whether a variable is of Boolean type. If so, it returns true, otherwise it returns false.

b. is_object()

is_object($var) is used to determine whether a variable is an object. If so, it returns true, otherwise it returns false.

c. is_array()

is_array($var) is used to determine whether a variable is an array. If so, it returns true, otherwise it returns false.

d. is_string()

is_string($var) is used to determine whether a variable is a string. If so, it returns true, otherwise it returns false.

e. is_numeric()

is_numeric($var) is used to determine whether a variable is numeric. If so, it returns true, otherwise it returns false.

5. Summary

This article introduces type conversion and type detection in PHP, including the rules of forced type conversion and automatic type conversion as well as some type detection functions. In development, using the correct type conversion function and type detection function can effectively avoid problems caused by type conversion. At the same time, when designing a program, you should also pay attention to the constraints of variable types to reduce the negative impact of weak type characteristics on the program.

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