PHP如何得到数组最后元素的key

1.array_keys(end($arr))

1. $array = array(
2. 'one'=>1,
3. 'two'=>2,
4. 'three'=>3,
5. 'four'=>4,
6. );
7. $arr = array_keys($array);
8. var_dump(end($arr));

2.array_pop(end($arr))

2. $array = array(
3. 'one'=>1,
4. 'two'=>2,
5. 'three'=>3,
6. 'four'=>4,
7. );
8. $arr = array_keys($array);
9. var_dump(array_pop($arr));

3.foreach()

1. $array = array(
2. 'one'=>1,
3. 'two'=>2,
4. 'three'=>3,
5. 'four'=>4,
6. );
7. foreach($array as $key => $value){
8. $temp = $key;
9. }
10. var_dump($temp)

4.array_slice

1. $array = array(
2. 'one'=>1,
3. 'two'=>2,
4. 'three'=>3,
5. 'four'=>4,
6. );
7. $arr = array_slice($array,-1,1,true);
8. var_dump(key($arr));