PHP output statement echo, print, Print_r, printf, sprintf, var_dump comparison

First, Echo
Echo () is not actually a function, it is a PHP statement, so you do not need to use parentheses on it. However, if you want to pass more than one argument to Echo (), a parse error occurs when you use parentheses. and echo returns void and does not return a value, so it cannot be used to assign a value.
Example:

<?php $a = Echo ("Xshell"); Error! Cannot be used to assign the echo "Xshell"; Xshell  Echo ("Xshell");//Xshell  Echo ("Xshell", "net");//error occurred, parentheses cannot pass multiple parameters  echo "Xshell", "net", "is", " Web ";  You can separate multiple values with commas without parentheses, and output Xshell NET is Web  echo "Xshell is  good  web.";  The final display is a line Xshell is good web, whether or not it wraps.  echo "$fistname net"; If $firstname = "Xshell", Xshell net is output.  Echo ' $firstname net '; Because of the use of single quotation marks, the $firstname value is not output, but the output $firstname net?>

Second, print
Print () is the same as Echo (), but the echo speed is a little bit faster than print. It is not actually a function, so you do not need to use parentheses on it. However, if you want to pass more than one parameter to print (), a parse error occurs when you use parentheses. Note that print always returns 1, which is different from Echo, which means you can use print to assign a value, but it doesn't make sense.
Example:

<?php$a = Print ("Xshell"); This is the allowed Echo $a; The value of the $a is 1?>

Three, Print_r function
The Print_r function prints easy-to-understand information about variables.
Syntax: Mixed print_r (mixed $expression [, BOOL return])
If the variable is a string, the integer or float will output its value directly, and if the variable is an array, it will output a formatted array for readability, which is the format of the key and value. Similar for object objects. Print_r has two parameters, the first is a variable, the second can be set to true, and if set to True, returns a string, otherwise returns a Boolean value of true.
Example:

<?php $a = "Xshell"; $c = Print_r ($a);  echo $c;  The value of $c is true  $c = Print_r ($a, ture);  Echo $c; The value of the $c is the string xshell?>

The

Four, printf functions
    printf function returns a formatted string.
    Syntax: printf (format,arg1,arg2,arg++)
    parameters format is the converted format, in percent notation ("%") Start to convert character end. The following is the possible format value:
*%%– Returns the percent symbol
*%b– binary number
*%c– characters in accordance with ASCII value
*%d– signed decimal number
*%e– sustainable counting method (e.g. 1.5e+3)
*%u– unsigned decimal number
*%f– floating point (Local settings Aware)
*%f– Floating-point number (not local settings aware)
*%o– octal
*%s– string
*%x– hexadecimal number (lowercase letter)
*%x– hexadecimal number (capital letter)
    arg1, arg2, arg++ and other parameters will be inserted into the main string percent percent (%) Symbol. The function is executed incrementally, in the first% symbol, insert arg1, insert arg2 at the second% symbol, and so on. 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 "\$". You can use numbers to specify the parameters that are displayed, see examples for details.
Example:

<?php printf ("My name is%s%s. "," Xshell "," net "); My name is Xshell net. printf ("My name is%1\ $s%1\ $s", "Xshell", "net"); Add 1\$ or 2\$ in front of s ..... Represents the position of the following parameter display, this line outputs My name is Ricky Ricky because only the first parameter is displayed two times. printf ("My name is%2\ $s%1\ $s", "Xshell", "net"); My name is Net Xshell?>

Five, sprintf function
This function uses the same method as printf, except that the function writes the formatted string to a variable instead of the output.
Example:

<?php sprintf ("My name is%1\ $s%1\ $s", "Xshell", "net");  You will find nothing to output.  $out = sprintf ("My name is%1\ $s%2\ $s", "Xshell", "net");  echo $out;  Output My name is Xshell net?>

Vi.. Var_dump function
Function: The content, type, and length of the output variable's contents, type, or string. Commonly used to debug.

<?php $a = 100; Var_dump ($a); Int (+) $a = 100.356; Var_dump ($a); Float (100.356)?>

PHP output statement echo, print, Print_r, printf, sprintf, var_dump comparison