Today i very much wondered, that if the string contain first letter has integer you can add that value into another integer variable.
$a = 20;
$b = "5doller";
$a+=$b;
echo $a;
Will any one can explain how this is happen and if i have like string like "dollar5" it wont add.
PHP is not strongly typed.
since the first character of your string is an integer and you are using the + operator it interprets the 5dollar as int and returns 25
example: http://en.wikipedia.org/wiki/Strong_typing#Example
PHP has a type conversion philosofy, that will auto convert the type of the data on runtime depending on the context. This may have it's advantages and disadvantages, and there are people against it and people who think it's ok (like in almost everything in life).
For more info about its behaviour please have a look on the php documentation: http://www.php.net/manual/en/language.types.type-juggling.php
It will try to see the string as an integer to ease your life if you use the arithmetic operator "+"(detecting the first character "5"), but leading to strange behaviours if not done properly.
That doesn't mean it doesn't have a type, $b is actually a string, only that it tries to convert it on runtime, but $b will still remain as a string.
To check this and/or prevent the strange behaviours you could use the php native functions to check the types:
$a = 20;
$b = "5doller";
if(is_integer($b)){
$a+=$b;
} elseif (is_string($b)) {
$a.=$b;
}
echo $a;
Or you can use gettype() which will return the variable type, and do a switch case or whatever you like to it. But in my opinion it would be over-coding, just use your common sense and be careful and normally it will be ok.
Even being relatively well aware of PHP peculiarities, the following strange behaviour still got me confused today:
// loose
$a = array(true => 'foo');
var_dump(array_key_exists(1, $a));
// strict
$a = array('7.1' => 'foo');
var_dump(array_key_exists('7.10', $a));
I wonder what could be the technical reason of this effect, so the question is, what in the process behind this function is causing values of some types to be compared loosely while others are compared strictly? I'm not complaining about the behaviour, but trying to understand that, so there is no point for "PHP sucks" comments.
In your first case, a boolean value is not a valid array key, so it is immediately turned into a 1 when you initialize the array, making your search match.
In your second case, the array key is a string, and '7.1' is not the same string as '7.10'
In your second example, '7.1' and '7.10' are strings. They are compared as string, so they don't match.
Now why do you have a match in the first example? Array keys can be either strings or integer. So true is converted to integer, which evaluates as 1.
This is documented here. Note that, keys are integers or strings. Specific key casts are mentioned in the documentation, in particular (for your case) that bools are cast to integers (ie. true as 1 and false as 0). As noted elsewhere, your other examples are strings (remove the quotes to make them floats, which would then be truncated to integers as per the docs).
maybe you could add the script output there? First glance though: Boolean as array key? I dont think thats gonna help in any way! 2nd: 7.10 is not the same at 7.1 - declaring this in '' makes it a string....
if you want true as a keyname, then you need to encapsulate it in either single or double quotes. IF you dont know about PHP and single/double quotes, it will cause the contents to be treated as a string value rather than Integer of Boolean (True/False)
I have a collegue who constantly assigns variable and forces their type. For example he would declare something like so:
$this->id = (int)$this->getId();
or when returning he will always return values as such:
return (int)$id;
I understand that php is a loosely typed language and so i am not asking what the casting is doing. I am really wondering what the benefits are of doing this - if any - or if he is just wasting time and effort in doing this?
There are a few benefits.
Type-checking. Without type-checking, 0 == false and 1 == true.
Sanitizing. If you're inserting the value into an SQL query, you can't have SQL injection because string values are converted to zero.
Integrity. It prevents inserting invalid database data. Again, it converts to zero, so you won't be trying to insert a string into a integer field in a database.
To explicitly convert a value to
integer, 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 integer
argument. A value can also be
converted to integer with the intval()
function.
http://www.php.net/manual/en/language.types.integer.php#language.types.integer.casting
PHP does not require (or support)
explicit type definition in variable
declaration; a variable's type is
determined by the context in which the
variable is used. That is to say, if a
string value is assigned to variable
$var, $var becomes a string. If an
integer value is then assigned to
$var, it becomes an integer.
An example of PHP's automatic type
conversion is the addition operator
'+'. If either operand is a float,
then both operands are evaluated as
floats, and the result will be a
float. Otherwise, the operands will be
interpreted as integers, and the
result will also be an integer. Note
that this does not change the types of
the operands themselves; the only
change is in how the operands are
evaluated and what the type of the
expression itself is.
http://www.php.net/manual/en/language.types.type-juggling.php
You can do something like this instead.
function hello($foo, $bar) {
assert(is_int($foo));
assert(is_int($bar));
}
http://php.net/manual/en/function.assert.php
PHP:
$a = "0";
$b = "00";
var_dump(empty($a)); # True (wtf?)
var_dump($a == $b); # True... WTF???
var_dump(empty($b)); # False WWWTTTFFFF!!??
I've read the docs. But the docs don't give explanation as to why they designed it this way. I'm not looking for workarounds (I already know them), I'm looking for an explanation.
Why is it like this? Does this make certain things easier somehow?
As for "0" == "00" resolving to true, the answer lies in Comparison Operators:
If you compare an integer with a
string, the string is converted to a
number. If you compare two numerical
strings, they are compared as
integers. These rules also apply to
the switch statement.
(emphasis added)
Both "0" and "00" are numerical strings so a numerical comparison is performed and obviously 0 == 0.
I'd suggest using === instead if you don't want any implicit type conversion.
As for empty():
The following things are considered to
be empty:
"" (an empty string)
0 (0 as an integer)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
var $var; (a variable declared, but without a value in a class)
http://au2.php.net/empty
The following things are considered to be empty:
"0" (0 as a string)
but "00" will not be considered empty.
It all stems from the language designers goal of "doing the right thing".
That is a given piece of code should do what the niave programmer or casual viewer of a piece of code would expect it too. This was not an easy goal to acheive.
Php has avoided most of worst pitfalls of other languages (like C's if (a = b) { ... or perl' s if ( "xxxx" == 0) { print "True!"; }).
The 0 == 0000 and if ("000") { echo "True!"; } are two of the few cases where code might not do exactly what you expect, but in pracice it is seldom a problem. In my experience the "cure" using the exact comparison operator === is the one thing guarenteed to have novice php programmers scratching there heads and searching the manual.
It has do do with what PHP considers empty, and, as #Shadow imagined, it's a dynamic typing issue. 0 and 00 are equal in PHP's eyes. Consider using the strict equality instead:
($a === $b) // is a equal to b AND the same type (strings)
Check the docs for empty http://us.php.net/empty. That should take care of the first and third lines.
for the second, it's because PHP is dynamically typed. the interpreter is inferring the type of the variables for use in the context in which you have used them. In this case the interpreter is probably thinking that you are trying to compare numbers and converting the string to ints before comparing.
From the documentation one can assume that 0 can be either an int or a 1 char string to signify empty. 00 would be more of a formatting assumption since there's no such thing as 00, but there is 0. 00 would be implying a 2 integer format, but the empty() function is only written for 0.
FWIW IANA php developer.
How do I convert the value of a PHP variable to string?
I was looking for something better than concatenating with an empty string:
$myText = $myVar . '';
Like the ToString() method in Java or .NET.
You can use the casting operators:
$myText = (string)$myVar;
There are more details for string casting and conversion in the Strings section of the PHP manual, including special handling for booleans and nulls.
This is done with typecasting:
$strvar = (string) $var; // Casts to string
echo $var; // Will cast to string implicitly
var_dump($var); // Will show the true type of the variable
In a class you can define what is output by using the magical method __toString. An example is below:
class Bottles {
public function __toString()
{
return 'Ninety nine green bottles';
}
}
$ex = new Bottles;
var_dump($ex, (string) $ex);
// Returns: instance of Bottles and "Ninety nine green bottles"
Some more type casting examples:
$i = 1;
// int 1
var_dump((int) $i);
// bool true
var_dump((bool) $i);
// string "1"
var_dump((string) 1);
Use print_r:
$myText = print_r($myVar,true);
You can also use it like:
$myText = print_r($myVar,true)."foo bar";
This will set $myText to a string, like:
array (
0 => '11',
)foo bar
Use var_export to get a little bit more info (with types of variable,...):
$myText = var_export($myVar,true);
You can either use typecasting:
$var = (string)$varname;
or StringValue:
$var = strval($varname);
or SetType:
$success = settype($varname, 'string');
// $varname itself becomes a string
They all work for the same thing in terms of Type-Juggling.
How do I convert the value of a PHP
variable to string?
A value can be converted to a string using the (string) cast or the strval() function. (Edit: As Thomas also stated).
It also should be automatically casted for you when you use it as a string.
You are looking for strval:
string strval ( mixed $var )
Get the string value of a variable.
See the documentation on string for
more information on converting to
string.
This function performs no formatting
on the returned value. If you are
looking for a way to format a numeric
value as a string, please see
sprintf() or number_format().
For primitives just use (string)$var or print this variable straight away. PHP is dynamically typed language and variable will be casted to string on the fly.
If you want to convert objects to strings you will need to define __toString() method that returns string. This method is forbidden to throw exceptions.
Putting it in double quotes should work:
$myText = "$myVar";
I think it is worth mentioning that you can catch any output (like print_r, var_dump) in a variable by using output buffering:
<?php
ob_start();
var_dump($someVar);
$result = ob_get_clean();
?>
Thanks to:
How can I capture the result of var_dump to a string?
Another option is to use the built in settype function:
<?php
$foo = "5bar"; // string
$bar = true; // boolean
settype($foo, "integer"); // $foo is now 5 (integer)
settype($bar, "string"); // $bar is now "1" (string)
?>
This actually performs a conversion on the variable unlike typecasting and allows you to have a general way of converting to multiple types.
In addition to the answer given by Thomas G. Mayfield:
If you follow the link to the string casting manual, there is a special case which is quite important to understand:
(string) cast is preferable especially if your variable $a is an object, because PHP will follow the casting protocol according to its object model by calling __toString() magic method (if such is defined in the class of which $a is instantiated from).
PHP does something similar to
function castToString($instance)
{
if (is_object($instance) && method_exists($instance, '__toString')) {
return call_user_func_array(array($instance, '__toString'));
}
}
The (string) casting operation is a recommended technique for PHP5+ programming making code more Object-Oriented. IMO this is a nice example of design similarity (difference) to other OOP languages like Java/C#/etc., i.e. in its own special PHP way (whenever it's for the good or for the worth).
As others have mentioned, objects need a __toString method to be cast to a string. An object that doesn't define that method can still produce a string representation using the spl_object_hash function.
This function returns a unique identifier for the object. This id can be used as a hash key for storing objects, or for identifying an object, as long as the object is not destroyed. Once the object is destroyed, its hash may be reused for other objects.
I have a base Object class with a __toString method that defaults to calling md5(spl_object_hash($this)) to make the output clearly unique, since the output from spl_object_hash can look very similar between objects.
This is particularly helpful for debugging code where a variable initializes as an Object and later in the code it is suspected to have changed to a different Object. Simply echoing the variables to the log can reveal the change from the object hash (or not).
I think this question is a bit misleading since,
toString() in Java isn't just a way to cast something to a String. That is what casting via (string) does, and it works as well in PHP.
// Java
String myText = (string) myVar;
// PHP
$myText = (string) $myVar;
Note that this can be problematic as Java is type-safe (see here for more details).
But as I said, this is casting and therefore not the equivalent of Java's toString().
toString in Java doesn't just cast an object to a String. It instead will give you the String representation. And that's what __toString() in PHP does.
// Java
class SomeClass{
public String toString(){
return "some string representation";
}
}
// PHP
class SomeClass{
public function __toString()
{
return "some string representation";
}
}
And from the other side:
// Java
new SomeClass().toString(); // "Some string representation"
// PHP
strval(new SomeClass); // "Some string representation"
What do I mean by "giving the String representation"?
Imagine a class for a library with millions of books.
Casting that class to a String would (by default) convert the data, here all books, into a string so the String would be very long and most of the time not very useful.
To String instead will give you the String representation, i.e., only the library's name. This is shorter and therefore gives you less, but more important information.
These are both valid approaches but with very different goals, neither is a perfect solution for every case, and you have to choose wisely which fits your needs better.
Sure, there are even more options:
$no = 421337 // A number in PHP
$str = "$no"; // In PHP, the stuff inside "" is calculated and variables are replaced
$str = print_r($no, true); // Same as String.format();
$str = settype($no, 'string'); // Sets $no to the String Type
$str = strval($no); // Get the string value of $no
$str = $no . ''; // As you said concatenate an empty string works too
All of these methods will return a String, some of them using __toString internally and some others will fail on Objects. Take a look at the PHP documentation for more details.
Some, if not all, of the methods in the previous answers fail when the intended string variable has a leading zero, for example, 077543.
An attempt to convert such a variable fails to get the intended string, because the variable is converted to base 8 (octal).
All these will make $str have a value of 32611:
$no = 077543
$str = (string)$no;
$str = "$no";
$str = print_r($no,true);
$str = strval($no);
$str = settype($no, "integer");
The documentation says that you can also do:
$str = "$foo";
It's the same as cast, but I think it looks prettier.
Source:
Russian
English
Double quotes should work too... it should create a string, then it should APPEND/INSERT the casted STRING value of $myVar in between 2 empty strings.
You can always create a method named .ToString($in) that returns
$in . '';
If you're converting anything other than simple types like integers or booleans, you'd need to write your own function/method for the type that you're trying to convert, otherwise PHP will just print the type (such as array, GoogleSniffer, or Bidet).
PHP is dynamically typed, so like Chris Fournier said, "If you use it like a string it becomes a string". If you're looking for more control over the format of the string then printf is your answer.
You can also use the var_export PHP function.
$parent_category_name = "new clothes & shoes";
// To make it to string option one
$parent_category = strval($parent_category_name);
// Or make it a string by concatenating it with 'new clothes & shoes'
// It is useful for database queries
$parent_category = "'" . strval($parent_category_name) . "'";
For objects, you may not be able to use the cast operator. Instead, I use the json_encode() method.
For example, the following will output contents to the error log:
error_log(json_encode($args));
Try this little strange, but working, approach to convert the textual part of stdClass to string type:
$my_std_obj_result = $SomeResponse->return->data; // Specific to object/implementation
$my_string_result = implode ((array)$my_std_obj_result); // Do conversion
__toString method or (string) cast
$string=(string)$variable; //force make string
you can treat an object as a string
class Foo
{
public function __toString()
{
return "foo";
}
}
echo new Foo(); //foo
also, have another trick, ı assume ı have int variable ı want to make string it
$string=''.$intvariable;
This can be difficult in PHP because of the way data types are handled internally. Assuming that you don't mean complex types such as objects or resources, generic casting to strings may still result in incorrect conversion. In some cases pack/unpack may even be required, and then you still have the possibility of problems with string encoding. I know this might sound like a stretch but these are the type of cases where standard type juggling such as $myText = $my_var .''; and $myText = (string)$my_var; (and similar) may not work. Otherwise I would suggest a generic cast, or using serialize() or json_encode(), but again it depends on what you plan on doing with the string.
The primary difference is that Java and .NET have better facilities with handling binary data and primitive types, and converting to/from specific types and then to string from there, even if a specific case is abstracted away from the user. It's a different story with PHP where even handling hex can leave you scratching your head until you get the hang of it.
I can't think of a better way to answer this which is comparable to Java/.NET where _toString() and such methods are usually implemented in a way that's specific to the object or data type. In that way the magic methods __toString() and __serialize()/__unserialize() may be the best comparison.
Also keep in mind that PHP doesn't have the same concepts of primitive data types. In essence every data type in PHP can be considered an object, and their internal handlers try to make them somewhat universal, even if it means loosing accuracy such as when converting a float to int. You can't deal with types as you can in Java unless your working with their zvals within a native extension.
While PHP userspace doesn't define int, char, bool, or float as an objects, everything is stored in a zval structure which is as close to an object that you can find in C, with generic functions for handling the data within the zval. Every possible way to access data within PHP goes down to the zval structure and the way the zend vm allows you to handles them without converting them to native types and structures. With Java types you have finer grained access to their data and more ways to to manipulate them, but also greater complexity, hence the strong type vs weak type argument.
These links my be helpful:
https://www.php.net/manual/en/language.types.type-juggling.php
https://www.php.net/manual/en/language.oop5.magic.php
I use variableToString. It handles every PHP type and is flexible (you can extend it if you want).