Edit Report a Bug

    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。

    和 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。

    示例

    示例 #1 print 示例

    <?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 6 * 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”
    ( 1 === 1 ) ? 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(1 + 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

    add a note add a note

    User Contributed Notes 3 notes

    up
    31
    user at example dot net
    16 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
    11
    danielxmorris @ gmail dotcom
    16 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
    1
    mark at manngo dot net
    1 year ago
    The other major difference with echo is that print returns a value, even it’s always 1.

    That might not look like much, but you can use print in another expression. Here are some examples:

    <?php
        rand    (0,1) ? print 'Hello' : print 'goodbye';
        print     PHP_EOL;
        print     'Hello ' and print 'goodbye';
        print     PHP_EOL;
            rand(0,1) or print 'whatever';
    ?>

    Here’s a more serious example:

    <?php
            function test() {
            return !!    rand(0,1);
        }
            test() or print 'failed';   
    ?>
    add a note add a note
    To Top