eval Evaluate a string as PHP code php函数


eval

(PHP 4, PHP 5)

evalEvaluate a string as PHP code

说明

mixed eval ( string $code_str )

Evaluates the string given in code_str as PHP code. Among other things, this can be useful for storing code in a database text field for later execution.

There are some factors to keep in mind when using eval(). Remember that the string passed must be valid PHP code, including things like terminating statements with a semicolon so the parser doesn't die on the line after the eval(), and properly escaping things in code_str. To mix HTML output and PHP code you can use a closing PHP tag to leave PHP mode.

Also remember that variables given values under eval() will retain these values in the main script afterwards.

参数

code_str

The code string to be evaluated. code_str does not have to contain PHP Opening tags.

A return statement will immediately terminate the evaluation of the string .

返回值

eval() returns NULL unless return is called in the evaluated code, in which case the value passed to return is returned. If there is a parse error in the evaluated code, eval() returns FALSE and execution of the following code continues normally. It is not possible to catch a parse error in eval() using set_error_handler().

范例

Example #1 eval() example - simple text merge

<?php
$string 
'cup';
$name 'coffee';
$str 'This is a $string with my $name in it.';
echo 
$str" ";
eval(
"$str = "$str";");
echo 
$str" ";
?>

以上例程会输出:

This is a $string with my $name in it.
This is a cup with my coffee in it.

注释

Note: 因为是一个语言构造器而不是一个函数,不能被 可变函数 调用。

Tip

和直接将结果输出到浏览器一样,可使用输出控制函数来捕获当前函数的输出,然后(例如)保存到一个 string 中。

Note:

In case of a fatal error in the evaluated code, the whole script exits.

参见

  • call_user_func() - Call a user function given by the first parameter



相关阅读:
exec Execute an external program
exif_imagetype 判断一个图像的类型
exif_read_data 从 JPEG 或 TIFF 文件中读取 EXIF 头信息
exif_tagname Get the header name for an index
exif_thumbnail 取得嵌入在 TIFF 或 JPEG 图像中的缩略图
exit Output a message and terminate the current script
exp 计算 e 的指数
explode 使用一个字符串分割另一个字符串
expm1 返回 exp(number)1,甚至当 number 的值接近零也能计算出准确结果
extension_loaded Find out whether an extension is loaded
extract 从数组中将变量导入到当前的符号表
ezmlm_hash 计算 EZMLM 所需的散列值
fbsql_affected_rows Get number of affected rows in previous FrontBase operation
fbsql_autocommit Enable or disable autocommit
快速导航

Copyright © 2016 phpStudy | 皖ICP备18014864号-4