Detailed explanation of the usage of php output string functions echo, print, printf, print_r and var_dump

In PHP, there are four ways to output strings. The echo structure can output multiple values ​​at one time; print() can only output one value; printf() can format the output; print_r() can output an array, which is very beneficial for debugging .

The following are introduced one by one.
1. echo
echo is a keyword in PHP, it has no return value. In terms of writing, it can omit the parentheses. The following code:

echo 'Test String'; 
echo('Test String');

2. print
print is also a keyword in PHP. It has a return value. It usually returns true, but there should be no return false. In terms of writing, it is the same as echo, and the parentheses can be omitted. The following code:

print 'Test String'; 
print('Test String');

3. printf
printf can format and output a string like printf in C language. Its format is similar to that of C language, both starting with %. Its specifier is defined below.
b The parameter is an integer and its binary number is displayed c The parameter is an integer and its corresponding ASCII character is displayed d The parameter is an integer and its decimal number is displayed
f The parameter is double precision and its decimal number is displayed It is a floating point number
e The parameter is double precision, displayed as scientific notation
g The parameter is double precision, displayed as floating point number or scientific notation
o The parameter is an integer, its octal number is displayed
s Parameters is a string, and is displayed as a string
u The parameter is an unsigned integer, and its decimal number is displayed
x/X The parameter is an integer, and its hexadecimal number is displayed (displayed in upper and lower case respectively)
% Output % It should be noted that:
f,e defaults to six digits after the decimal point. When g exceeds six digits (plus decimal point), it will be rounded. If the rounded value is less than 1000000, it will be output directly. If it is greater than 1000000, it will be displayed as scientific Counting type. When the value of f is greater than 1.2e23, the output result is incorrect.
Except for %, the total number of output digits can be specified (decimal point, E counts as one), 0 or a space can be specified as the complement character, and the complement character can also be specified on the left or right.
f, e can specify the number of digits after the decimal point.
For example, %5d means that the total number of output digits is 5, and the remaining digits are left filled with spaces; %05d means that the total number of output digits is 5, and the remaining digits are left filled with 0s; %05.1f means that the total number of output digits is 5, and the remaining digits are left filled with 0s. 1 digit after the decimal point; %-05.1f means that the total number of output digits is 5, any missing digits are padded to the right with 0, and 1 digit after the decimal point;
Sample code:

printf("%7.2f", 1.2); // " 1.20" 
printf("%-07.2f", 1.2); // "1.20000"

4.

sprintf sprintf and format conversion are the same as printf. The difference between the two is that printf outputs directly, while sprintf returns a formatted string.
5. print_r and var_dump
Both print_r and var_dump can output arrays and objects, but print_r's output of Boolean types is not obvious; var_dump's output is more detailed and is generally used during debugging. The following code:

$v = new test(); 
print_r($v); 
var_dump($v); 
class test { 
public $num = 1; 
public $str = "222"; 
public $bln = true;

The result is:

test Object 
( 
[num] => 1 
[str] => 222 
[bool] => 1 
) 
object(test)#1 (3) { 
["num"]=> 
int(1) 
["str"]=> 
string(3) "222" 
["bool"]=> 
bool(true) 
}

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