Precautions for using the empty () function in php

When empty () is used to determine the number 0, empty () returns true, that is, if your variable may contain the number 0, you must use isset () will be better !!

On the surface, it is easy to misunderstand that the empty () function is a function used to judge whether the string is null. In fact, it is not, so I suffered a lot of losses.

The empty () function is used to test whether the variable has been configured. If the variable already exists, non-null string, or non-zero, false is returned; otherwise, true is returned. Therefore, if the value of the string is 0, true is returned, that is, the internal statement of empty is executed. This is a trap.

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$ A = array ("1" => "ddf "); Var_dump (empty ($ a); // boolean false $ B = 0; Var_dump (empty ($ B); // boolean true

We advise you to use the empty () function.

To judge whether the string is null, you can judge it as follows: if ($ value = "")...
* Format: bool empty (mixed var)
* Function: Check whether a variable is empty.
* Return value:
* Returns TRUE if the variable does not exist.
* If a variable exists and its values are "", 0, "0", NULL, FALSE, array (), var $ var, and objects without any attribute, true is returned.
* If a variable exists and its values are not "", 0, "0", NULL, FALSE, array (), var $ var, or an object without any attribute, FALSE is returned.
* Version: PHP 3, PHP 4, and PHP 5

On the surface, it is easy to misunderstand that the empty () function is a function used to judge whether the string is null. In fact, it is not, so I suffered a lot of losses. The empty () function is used to test whether the variable has been configured. If the variable already exists, non-null string, or non-zero, false is returned; otherwise, true is returned. Therefore, if the value of the string is 0, true is returned, that is, the internal statement of empty is executed. This is a trap. For example, suppose $ value = 0; then empty ($ value) = false. We advise you to use the empty () function. To judge whether the string is null, you can judge it as follows: if ($ value = "")... format: bool empty (mixed var) function: checks whether a variable has a NULL return value: if the variable does not exist, TRUE is returned. If the variable exists, its values are "", 0, "0", NULL, FALSE, array (), and var $ var; if the variable exists and the value is not "", 0, "0", NULL, FALSE, array (), var $ var; if the object does not have any attribute, FALSE versions are returned: PHP 3, PHP 4, and PHP 5.

When you use empty to check the results returned by a function, the following error occurs: Fatal error: Can't use function return value in write context.

For example:

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<? Php Echo empty (strlen ('be -evil.org '));

Go to the PHP manual and check the following text in the description of the empty function:

Note: empty () only checks variables as anything else will result in a parse error. In other words, the following will not work: empty (trim ($ name )).

Empty () only detects variables, and any non-variables will cause parsing errors!

Therefore, we cannot use empty to directly detect the values returned by the function. The solution in the preceding example is as follows:

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<? Php $ Length = strlen ('be -evil.org '); Echo empty ($ length ); ?>