判断是否为空之后的操作

$buf = array($a, $b, $c, $d);echo join(',', array_filter($buf, 'cmp'));function cmp($m) {  return ! empty($m);}

$s = "$a,$b,$c,$d";$ar = preg_split('/,/', $s, -1, PREG_SPLIT_NO_EMPTY);echo implode(',', $ar);

$a = 'a';$b = '';$c = '';$d = 'd';echo handle($a,$b,$c,$d);function handle($a,$b,$c,$d){    $arr = array();    array_push($arr, $a,$b,$c,$d);    $ret = trim(implode(',', $arr),',');    $ret = preg_replace('/[,]{2,}/', ',', $ret);    return $ret;}

$a = 'a';$b = 'b';$c = 'c';$d = 'd';$arr = array($a,$b,$c,$d);$ret = array();foreach($arr as $val){    if($val!=''){        array_push($ret, $val);    }}echo implode(',', $ret);