the way of output an array's variable

how many ways we can do to output an array's variable,
eg:$row=array{...}

as far as i know,the followings are the output format,which is right?and why?

echo $row[$key];
echo $row[key];
echo $row['key'];
i have tested the echo $row[$key]; is wrong, and what is the difference of the rest.thank you!

 

who can explain?
thank you

 

print_r($row);

 

If you want nicer output to debug, try the function below (not written by me btw)

function print_nice($elem,$max_level=10,$print_nice_stack=array()){
    if(is_array($elem) || is_object($elem)){
        if(in_array(&$elem,$print_nice_stack,true)){
            echo "<font color=red>RECURSION</font>";
            return;
        }
        $print_nice_stack[]=&$elem;
        if($max_level<1){
            echo "<font color=red>nivel maximo alcanzado</font>";
            return;
        }
        $max_level--;
        echo "<table border=1 cellspacing=0 cellpadding=3 width=100%>";
        if(is_array($elem)){
            echo '<tr><td colspan=2 style="background-color:#333333;"><strong><font color=white>ARRAY</font></strong></td></tr>';
        }else{
            echo '<tr><td colspan=2 style="background-color:#333333;"><strong>';
            echo '<font color=white>OBJECT Type: '.get_class($elem).'</font></strong></td></tr>';
        }
        $color=0;
        foreach($elem as $k => $v){
            if($max_level%2){
                $rgb=($color++%2)?"#888888":"#BBBBBB";
            }else{
                $rgb=($color++%2)?"#8888BB":"#BBBBFF";
            }
            echo '<tr><td valign="top" style="width:40px;background-color:'.$rgb.';">';
            echo '<strong>'.$k."</strong></td><td>";
            print_nice($v,$max_level,$print_nice_stack);
            echo "</td></tr>";
        }
        echo "</table>";
        return;
    }
    if($elem === null){
        echo "<font color=green>NULL</font>";
    }elseif($elem === 0){
        echo "0";
    }elseif($elem === true){
        echo "<font color=green>TRUE</font>";
    }elseif($elem === false){
        echo "<font color=green>FALSE</font>";
    }elseif($elem === ""){
        echo "<font color=green>EMPTY STRING</font>";
    }else{
        echo str_replace("\n","<strong><font color=red>*</font></strong><br>\n",$elem);
    }
}

PHP:

 

And for nice formating in browserL

echo "<pre>";
print_r($row);
echo "</pre>";

PHP:

 

can just view source

 

echo $row[$key]; doesn't make sense, it's supposed to be used for assignment only when you want to force a key for an array value, e.g. instead of seeing Array([0] => 'blah') you would see Array([keyval] => 'blah').

echo $row[key]; works, just uses slightly more memory than using

echo $row['key'];

 

Please learn more php.