The difference between PHP echo, print_r(expression), var_dump(expression), print_rvar_dump_PHP tutorial

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

All three are PHP statements with output function, but print_r(expression), var_dump(expression) is a function, echo is just a language structure, not a function, so it cannot be used as part of the expression.
For php’s 8 data types,

What data types can echo, print_r and var_dump in PHP output? How are they different?

echo 'Output a string';//Only strings and numbers can be output

print_r — Print easy-to-understand information about variables, generally using the output array structure

var_dump — Print relevant information about variables, generally used for array and object printing

You will know it after using it yourself

What are the differences between echo(), print(), and print_r() in PHP?

Four ways to output strings. echo

print()

printf()

print_r()
echo
can output multiple values ​​at one time, separated by commas . echo is a language construct, not a real function, so it cannot be used as part of an expression.

Correct syntax: echo "Hello", "World";
Wrong syntax: echo ("Hello", "World");
print()
The function print() prints a Value (its argument), returns true if the string was successfully displayed, false otherwise. For example, if (!print("Hello, World")){

die("you are not listening to me");

}
printf()
printf () originates from printf() in C language. This function outputs a formatted string.
Syntax: printf(format,arg1,arg2,arg++)
format specifies the string and how to format the variables in it;
arg1, arg2, ++ and other parameters will be inserted into the main string Semicolon (%) symbol. This function is executed step by step. At the first % sign, arg1 is inserted, at the second % sign, arg2, and so on.
Example: ?php

$str = "Hello";

$number = 123;

printf("%s world. Day number %u", $str,$number);

?>
#Results======
Hello world. Day number 123

If there are more % symbols than arg parameters, then you must use placeholders. Placeholders are inserted after the % sign and consist of numbers and "\$". 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 out strings and numbers, while arrays are displayed as a bracketed list of keys and values, starting with Array. For example, $a = array('name' => 'Fred', 'age' => '15', 'wife' => 'Wilma');

print_r($a);
Output: Array

{

[name] => Fred

[age] => 15

[wife] => ; The same goes for Wilma

}
objects. For example, class P {

var $name = 'nat';

// ...

}

$p = new P;

print_r($p);
Output: Object

{

[name] => nat

}
but print_r( ) The results of outputting Boolean values ​​and NULL are meaningless, because they all print "...the rest of the full text>>

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