Differences between empty, isset, and is_null in PHP
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In PHP, empty, isset, and is_null are different. if the variable is not null or a non-zero value, empty () returns FALSE. In other words, "", 0, "0", NULL, FALSE, array (), var $ var, undefined; and no difference between empty, isset, and is_null in PHP
If the variable is not null or a non-zero value, empty () returns FALSE. In other words, "", 0, "0", NULL, FALSE, array (), var $ var, undefined, and objects without any attributes will be considered empty, if var is null, TRUE is returned.
If the variable exists (not NULL), TRUE is returned; otherwise, FALSE (including undefined) is returned ). If the value of a variable is set to null, false is returned. if a variable is unset, the variable is canceled. Note that isset has special processing for NULL variables.
Checks whether the input value [value, variable, expression] is null. only if one variable is defined and its value is null, TRUE is returned. otherwise, FALSE is returned. [an error will occur after an undefined variable is passed in! ].
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