PHP补全固定数字位数前面有0的值

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1->0001 
56->0056 
288->0288 
1992->1992
//        echo sprintf("%04d", $num+1);
        echo str_pad($num,4,"0",STR_PAD_LEFT);//4是固定位数，0是要加的固定值，STR_PAD_LEFT是左边插入，末尾加用STR_PAD_RIGHT

$num=123;

$num=str_pad($num,4,"0",STR_PAD_LEFT);

echo $num;

结果为：0123

以上皆可