print

(PHP 4, PHP 5, PHP 7, PHP 8)

print输出字符串

说明

print(string $expression): int

输出 expression

print 不是函数而是语言结构。它的参数是跟在 print 关键字后面的表达式,并且不用括号分割。

echo 最主要的区别是 print 仅接受一个参数,并始终返回 1

参数

expression

要输出的表达式。即使启用 strict_types 指令,非字符串也会强制转换为字符串。

返回值

总是返回 1

范例

示例 #1 print 范例

<?php
print "print does not require parentheses.";

// 不会新增新行或者空格;下面会在一行中输出“helloworld”
print "hello";
print 
"world";

print 
"This string spans
multiple lines. The newlines will be
output as well"
;

print 
"This string spans\nmultiple lines. The newlines will be\noutput as well.";

// 参数可以是任何生成字符串的表达式
$foo "example";
print 
"foo is $foo"// foo is example

$fruits = ["lemon""orange""banana"];
print 
implode(" and "$fruits); // lemon and orange and banana

// 即使使用了 declare(strict_types=1),非字符串表达式也会强制转换为字符串
print 7// 42

// 因为 print 有返回值,所以可以在如下表达式中使用
// 以下输出“hello world”
if ( print "hello" ) {
    echo 
" world";
}

// 以下输出“true”
=== ) ? print 'true' : print 'false';
?>

注释

注意: 使用括号

用括号括住 print 的参数并不会引发语法错误,而且会产生看起来像是普通函数调用的语法。然而,这可能会产生误导,因为括号实际上是输出表达式的一部分,而非 print 语法本身的一部分。

<?php
print "hello";
// 输出“hello”

print("hello");
// 也会输出“hello”,因为 ("hello") 是有效的表达式

print(2) * 3;
// 输出“9”;会首先对括号内的 1+2 进行求值,然后是 3*3
// print 语句会将整个表达式视为一个参数

if ( print("hello") && false ) {
    print 
" - inside if";
}
else {
    print 
" - inside else";
}
// 输出“ - inside if”
// 首先对表达式 ("hello") && false 求值, false
// 强制转换为空字符串“”且打印 print 
// 结构,然后返回 1,所以运行 if 块中代码
?>

当在大表达式中使用 print 时,需要将关键字及其参数放在括号中以便得出预期的结果:

<?php
if ( (print "hello") && false ) {
    print 
" - inside if";
}
else {
    print 
" - inside else";
}
// 输出“hello - inside else”
// 跟上个示例不同,首先对表达式 (print "hello") 求值
// 输出“hello”之后,print 返回 1
// 由于 1 && false 为 false,因此运行 else 块中代码

print "hello " && print "world";
// 输出“world1”;首先对 print "world" 求值,
// 然后表达式 "hello " && 1 传递给左侧的 print

(print "hello ") && (print "world");
// 输出“hello world”;括号强制 print 表达式
// 在 && 之前求值
?>

注意: 因为是语言构造器而不是函数,不能被 可变函数 或者 命名参数 调用。

参见

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User Contributed Notes 9 notes

up
30
user at example dot net
14 years ago
Be careful when using print. Since print is a language construct and not a function, the parentheses around the argument is not required.
In fact, using parentheses can cause confusion with the syntax of a function and SHOULD be omited.

Most would expect the following behavior:
<?php
   
if (print("foo") && print("bar")) {
       
// "foo" and "bar" had been printed
   
}
?>

But since the parenthesis around the argument are not required, they are interpretet as part of the argument.
This means that the argument of the first print is

    ("foo") && print("bar")

and the argument of the second print is just

    ("bar")

For the expected behavior of the first example, you need to write:
<?php
   
if ((print "foo") && (print "bar")) {
       
// "foo" and "bar" had been printed
   
}
?>
up
14
danielxmorris @ gmail dotcom
14 years ago
I wrote a println function that determines whether a \n or a <br /> should be appended to the line depending on whether it's being executed in a shell or a browser window.  People have probably thought of this before but I thought I'd post it anyway - it may help a couple of people.

<?php
function println ($string_message) {
   
$_SERVER['SERVER_PROTOCOL'] ? print "$string_message<br />" : print "$string_message\n";
}
?>

Examples:

Running in a browser:

<?php println ("Hello, world!"); ?>
Output: Hello, world!<br />

Running in a shell:

<?php println ("Hello, world!"); ?>
Output: Hello, world!\n
up
5
jon
15 years ago
the FAQTs article can be found archived at http://web.archive.org/web/20060601063513/http
://www.faqts.com/knowledge_base/view.phtml/aid/1/fid/40

(url split to get past the line-length limitation)
up
1
Chris Watson
13 years ago
mvpetrovich of 2007 could just use single quotes as his string delimiters (see the example in the current documentation).
It's not ALWAYS appropriate, but generally it is best (the Zend Framework coding standards have a good take on this). It yields a number of interesting benefits:
1: Nobody will be tempted to write functions to replace backticks or other characters with double quotes. Such functions may cause a (negligible) loss of efficiency, and maybe other undesired effects.
2: You will be able to use double quotes without escaping. This is recommended (although not required) for HTML and XML attributes, as well as quoted text.
3: The script will hit the browser very slightly slightly faster since PHP doesn't have to scan through the string looking for variables, escaped characters, curly braces or other things.
4: Your code gets ten times easier to read. (as mvpetrovich pointed out)

If, in spite of these four excellent benefits, you really MUST still use double quotes to delimit boring old string constants (and seriously, why would you?), you could use the slightly less favourable single quotes as delimiters for most markup languages.
HTML served as HTML will even let you lay out unquoted attributes (yuck).

It should also be noted though that if you are just printing bare strings, you may as well shut off the php parser. The quickest way to send a string is to write it as plain text, OUTSIDE of the php tags. This will also make your code look excellent in a lot of syntax highlighters.

There are few disadvantages to doing this, if any. Output buffering still works. All your classes and objects and includes remain in place. Your script runs faster. World peace is obtained.
up
0
jon at tap dot net
17 years ago
I have a small utility run from the command line that processes a potentially huge list of files. As it can take hours to complete, I stuck a 

print '.';

statement in the body of the main loop to prove that something was  happening.

For reasons unknown to me, the utiliity suddenly started buffering the output such that it printed nothing until completion, defeating the purpose of the running monitor. Adding flush() statements did nothing. The problem was solved by using

fputs(STDOUT, '.');

but I have no idea why.
up
-1
dkrupyanskiy
4 years ago
Don't rely on parenthesis used for `print` construct:

print 1 . print(2) + 3;
print PHP_EOL;
print 1 . (print(2)) + 3;
up
-2
phpnet at i3x171um dot com
16 years ago
I have written a script to benchmark the several methods of outputting data in PHP: via single quotes, double quotes, heredoc, and printf. The script constructs a paragraph of text with each method. It performs this construction 10,000 times, then records how long it took. In total, it prints 160,000 times and records 16 timings. Here are the raw results.

Outputted straight to browser--

Single quotes: 2,813 ms
...with concatenation: 1,179 ms
Double quotes: 5,180 ms
...with concatenation: 3,937 ms
heredoc: 7,300 ms
...with concatenation: 6,288 ms
printf: 9,527 ms
...with concatenation: 8,564 ms

Outputted to the output buffer--

Single quotes: 8 ms
...with concatenation: 38 ms
Double quotes: 8 ms
...with concatenation: 47 ms
heredoc: 17 ms
...with concatenation: 49 ms
printf: 54 ms
...with concatenation: 52 ms

A nice graph of the script's output can be found here:
http://i3x171um.com/output_benchmarks/ob.gif

So what should you choose to print your text? I found several things out writing this.

First, it should be noted that the print and echo keywords are interchangeable, performance-wise. The timings show that one is probably an alias for the other. So use whichever you feel most comfortable with.

Second, if you've ever wondered which was better, the definitive answer is single quotes. Single quotes are at least four times faster in any situation. Double quotes, while more convenient, do pose a debatably significant performance issue when outputting massive amounts of data.

Third, stay away from heredoc, and absolutely stay away from [s]printf. They're slow, and the alternatives are there.

The source of my script can be found here:
http://i3x171um.com/output_benchmarks/ob.txt

DO NOT RUN THE SCRIPT ON THE INTERNET! Run it instead from localhost. The script outputs ~45 megabytes of text in an html comment at the top of the page by default. Expect the benchmark to take ~45 seconds. If this is too long, you can change the amount of iterations to a lower number (the results scale accurately down to about 1,000 iterations).
up
-5
ejallison at gmail dot com
17 years ago
This is a simple function for printing debug comments that I didn't think of for a long time. Maybe it'll serve you good too.

<?php

function printd($str) {
  if (
$debug) { echo $str; }
}

// ...

if ($valueCalculatedEarlierInTheScript == 3) {
 
doSomethingWithNoOutput();
 
printd("doSomethingWithNoOutput() has executed.");
}

?>

It's mostly just to make sure everything is running without having to go through everything and put in echo "Step #whatever has executed" whenever something mysterious isn't working.
up
-9
http://www.danielxmorris.com
14 years ago
An update to the println function I wrote below, this is a more efficient, correct and returns a value (1, always; (print)).

<?php

   
function println($string_message = '') {
        return isset(
$_SERVER['SERVER_PROTOCOL']) ? print "$string_message<br />" . PHP_EOL:
          print
$string_message . PHP_EOL;
    }

?>
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