PHP echo,print_r (expression), var_dump (expression) difference, print_rvar_dump_php tutorial

PHP echo,print_r (expression), var_dump (expression) difference, print_rvar_dump

All three are PHP statements with output functionality, but print_r (expression), var_dump (expression) is a function, and Echo is simply a language structure, not a function, and therefore cannot be part of an expression.
For the 8 data types in PHP,

What kind of data can I output in PHP echo,print_r,var_dump? What difference do they have?

Echo ' outputs a string ';//can only output strings and numbers

print_r-Print easy-to-understand information about variables, typically with an output array structure

var_dump-information about printing variables, typically used for array and object printing

It's clear that you use it yourself.

What is the difference between echo (), print (), and Print_r () in PHP?

There are four ways to output a string. Echo

Print ()

printf ()

Print_r ()
Echo
Multiple values can be output at one time, and multiple values are separated by commas. Echo is a language structure (language construct), not a real function and therefore cannot be used as part of an expression.

Grammatically correct: Echo "Hello", "World";
Syntax error: Echo ("Hello", "World");
Print ()
The function print () prints a value (its arguments) and returns True if the string is successfully displayed, otherwise false. For example, if (!print ("Hello, World")) {

Die ("is not a listening to me");

}
printf ()
printf () originates from printf () in the C language. The function outputs a formatted string.
Syntax: printf (format,arg1,arg2,arg++)
format Specifies the string and how the variable is formatted;
Arg1, arg2, + + etc parameters will be inserted into the main string percent percent (%) Symbol. This function is executed step-by. In the first% symbol, insert arg1, insert arg2 at the second% symbol, and so on.
Example:? php

$str = "Hello";

$number = 123;

printf ("%s World". Day number%u ", $STR, $number);

?>
#Results ======
Hello World. Day Number 123

If the% symbol is more than the arg parameter, you must use a placeholder. After the placeholder is inserted in the% symbol, it consists of a number and a "\$". See Example 3.
Example:? php

$number = 123;

printf ("With 2 decimals:%1\$.2FBR/>with no decimals:%1\ $u", $number);

?>
#Result
With 2 decimals:123.00
With no decimals:123

Print_r () and Var_dump ()
Print_r () can simply print the string and the number, and the array is displayed with the enclosed key and the list of merit, beginning with an array. For example, $a = Array (' name ' = ' Fred ', ' age ' = ' + ', ' wife ' = ' Wilma ');

Print_r ($a);
Output:array

{

[Name] + Fred

[Age] = 15

[Wife] = Wilma

}
objects are the same. For example, class P {

var $name = ' nat ';

// ...

}

$p = new P;

Print_r ($p);
Output:object

{

[Name] = NAT

}
But the result of Print_r () output Boolean and null is meaningless, because all are printed &quo ... Remaining full text >>

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