特定if语句的含义

Question

What is the different meaning of the if-statement ( if(condition -> condition) ) to the regular if-statement ( if(condition = condition)) ?

looking up for the meaning without success.

if ($erg->num_rows) {
    echo "<p>Daten vorhanden: Anzahl ";
    echo $erg->num_rows;

Answer 1

If you are familiar with OOP concepts in PHP, then you will be able to understand what is going on here, else I recommend you to firstly get your hands dirty with OOP in PHP

Here $erg->num_rows is not a condition. -> operator is used to access any attribute of the pointing class instance.

In simple words, this line:

if ($erg->num_rows)

checks if the number of rows is greater than zero (as suggested by the variable name), if yes then the following code will be executed.

Because 0 is false and any other number is true. That means if $erg->num_rows returns 0 then condition will be evaluated to false and if it returns value that is not 0, then condition will be evaluated to true.

-> operator has nothing to do with if statements.