全局变量$_POST[name]的引用哪个写法正确?
$_POST[pwd]
$_POST['pwd']
$_POST["pwd"]PS:本人初学PHP,原有C语言基础,感觉PHP语言的语句规范没有C那么严谨,而且教材(《PHP从入门到精髓》)错漏百出,感觉挺别扭的,有没有什么权威的资料可以查询的?
$_POST[pwd]
$_POST['pwd']
$_POST["pwd"]PS:本人初学PHP,原有C语言基础,感觉PHP语言的语句规范没有C那么严谨,而且教材(《PHP从入门到精髓》)错漏百出,感觉挺别扭的,有没有什么权威的资料可以查询的?
<?php
$foo[bar] = 'enemy';
echo $foo[bar];
// etc
?>
这样是错的,但可以正常运行。那么为什么错了呢?原因是此代码中有一个未定义的常量(bar)而不是字符串('bar'-注意引号),而 PHP 可能会在以后定义此常量,不幸的是你的代码中有同样的名字。它能运行,是因为 PHP 自动将裸字符串(没有引号的字符串且不对应于任何已知符号)转换成一个其值为该裸字符串的正常字符串。例如,如果没有常量定义为 bar,PHP 将把它替代为 'bar' 并使用之。 注: 这并不意味着总是给键名加上引号。用不着给键名为常量或变量的加上引号,否则会使 PHP 不能解析它们。
<?php
error_reporting(E_ALL);
ini_set('display_errors', true);
ini_set('html_errors', false);
// Simple array:
$array = array(1, 2);
$count = count($array);
for ($i = 0; $i < $count; $i++) {
echo "\nChecking $i: \n";
echo "Bad: " . $array['$i'] . "\n";
echo "Good: " . $array[$i] . "\n";
echo "Bad: {$array['$i']}\n";
echo "Good: {$array[$i]}\n";
}
?>
注: 上例将输出:Checking 0:
Notice: Undefined index: $i in /path/to/script.html on line 9
Bad:
Good: 1
Notice: Undefined index: $i in /path/to/script.html on line 11
Bad:
Good: 1Checking 1:
Notice: Undefined index: $i in /path/to/script.html on line 9
Bad:
Good: 2
Notice: Undefined index: $i in /path/to/script.html on line 11
Bad:
Good: 2
演示此效应的更多例子:
<?php
// 显示所有错误
error_reporting(E_ALL);$arr = array('fruit' => 'apple', 'veggie' => 'carrot');// 正确
print $arr['fruit']; // apple
print $arr['veggie']; // carrot// 不正确。This works but also throws a PHP error of
// level E_NOTICE because of an undefined constant named fruit
//
// Notice: Use of undefined constant fruit - assumed 'fruit' in...
print $arr[fruit]; // apple// Let's define a constant to demonstrate what's going on. We
// will assign value 'veggie' to a constant named fruit.
define('fruit','veggie');// Notice the difference now
print $arr['fruit']; // apple
print $arr[fruit]; // carrot// The following is okay as it's inside a string. Constants are not
// looked for within strings so no E_NOTICE error here
print "Hello $arr[fruit]"; // Hello apple// With one exception, braces surrounding arrays within strings
// allows constants to be looked for
print "Hello {$arr[fruit]}"; // Hello carrot
print "Hello {$arr['fruit']}"; // Hello apple// This will not work, results in a parse error such as:
// Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING'
// This of course applies to using autoglobals in strings as well
print "Hello $arr['fruit']";
print "Hello $_GET['foo']";// Concatenation is another option
print "Hello " . $arr['fruit']; // Hello apple
?> 当打开 error_reporting() 来显示 E_NOTICE 级别的错误(例如将其设为 E_ALL)时将看到这些错误。默认情况下 error_reporting 被关闭不显示这些。
$abc='my name is tome';
echo $abc //结果是:my name is tom
echo '$abc' //结果是:$abc
echo "$abc" //结果是:my name is tom