字符串运算符

    有两个字符串（string）运算符。第一个是连接运算符（“.”），它返回其左右参数连接后的字符串。第二个是连接赋值运算符（“.=”），它将右边参数附加到左边的参数之后。更多信息见赋值运算符。

    <?php
    $a     = "Hello ";
    $b = $a . "World!"; // 现在 $b 包含 "Hello World!"

    $a = "Hello ";
    $a .= "World!"; // 现在 $a 包含 "Hello World!"
    ?>

    参见

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    用户贡献的备注 6 notes

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    262
    K.Alex
    11 years ago
    As for me, curly braces serve good substitution for concatenation, and they are quicker to type and code looks cleaner. Remember to use double quotes (" ") as their content is parced by php, because in single quotes (' ') you'll get litaral name of variable provided:

    <?php

    $a     = '12345';

    // This works:
    echo "qwe{$a}rty"; // qwe12345rty, using braces
    echo "qwe" . $a . "rty"; // qwe12345rty, concatenation used

    // Does not work:
    echo 'qwe{$a}rty'; // qwe{$a}rty, single quotes are not parsed
    echo "qwe$arty"; // qwe, because $a became $arty, which is undefined

    ?>
    up
    168
    anders dot benke at telia dot com
    20 years ago
    A word of caution - the dot operator has the same precedence as + and -, which can yield unexpected results.

    Example:

    <php
    $var = 3;

    echo "Result: " . $var + 3;
    ?>

    The above will print out "3" instead of "Result: 6", since first the string "Result3" is created and this is then added to 3 yielding 3, non-empty non-numeric strings being converted to 0.

    To print "Result: 6", use parantheses to alter precedence:

    <php
    $var = 3;

    echo "Result: " . ($var + 3);
    ?>
    up
    109
    Stephen Clay
    18 years ago
    <?php
    "{$str1}{$str2}{$str3}"; // one concat = fast
    $str1. $str2. $str3; // two concats = slow
    ?>
    Use double quotes to concat more than two strings instead of multiple '.' operators. PHP is forced to re-concatenate with every '.' operator.
    up
    89
    hexidecimalgadget at hotmail dot com
    15 years ago
    If you attempt to add numbers with a concatenation operator, your result will be the result of those numbers as strings.

    <?php

    echo "thr"."ee"; //prints the string "three"
    echo "twe" . "lve"; //prints the string "twelve"
    echo 1 . 2; //prints the string "12"
    echo 1.2; //prints the number 1.2
    echo 1+2; //prints the number 3

    ?>
    up
    7
    biziclop
    2 years ago
    Some bitwise operators (the and, or, xor and not operators: & | ^ ~ ) also work with strings too since PHP4, so you don't have to loop through strings and do chr(ord($s[i])) like things.

    See the documentation of the bitwise operators: https://www.php.net/operators.bitwise

    <?php var_dump(
    (    '23456787654' ^ 'zVXYYhoXDYP'), // 'Hello_World'
    ('(!($)^!)@$@' | '@ddhfIvn2H$'), // 'hello_world'
    ('{}~|o!Wo{|}' & 'Lgmno|Wovmf'), // 'Hello World'
    (~'<0-14)(98' & '}}}}}}}}}') // 'AMPLITUDE'
    ); ?>

    Live demo: https://3v4l.org/MnFeb
    up
    39
    mariusads::at::helpedia.com
    16 years ago
    Be careful so that you don't type "." instead of ";" at the end of a line.

    It took me more than 30 minutes to debug a long script because of something like this:

    <?
    echo 'a'.
    $c = 'x';
    echo     'b';
    echo     'c';
    ?>

    The output is "axbc", because of the dot on the first line.
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