PHP array_splice函数使用方法
本文介绍了php中array_slice和array_splice函数解析,php拆分数组的二个函数(array_slice()、array_splice()),各举一个例子,供大家学习参考。
array_slice和array_splice函数是用在取出数组的一段切片,array_splice还有用新的切片替换原删除切片位置的功能。类似javascript中的Array.prototype.splice和Array.prototype.slice方法。
array_slice
array array_slice ( array $array , int $offset [, int $length = NULL [, bool $preserve_keys = false ]] )
返回数组中指定下标offset和长度length的子数组切片。
参数说明
设第一个参数数组的长度为num_in。
offset
如果offset是正数且小于length,则返回数组会从offset开始;如果offset大于length,则不操作,直接返回。如果offset是负数,则offset = num_in+offset,如果num_in+offset == 0,则将offset设为0。
length
如果length小于0,那么会将length转为num_in - offset + length;否则,如果offset+length > array_count,则length = num_in - offset。如果处理后length还是小于0,则直接返回。
preserve_keys
默认是false,默认不保留数字键值原顺序,设为true的话会保留数组原来的数字键值顺序。
使用实例
<?php $input = array("a", "b", "c", "d", "e"); $output = array_slice($input, 2); // returns "c", "d", and "e" $output = array_slice($input, -2, 1); // returns "d" $output = array_slice($input, 0, 3); // returns "a", "b", and "c" print_r(array_slice($input, 2, -1)); // array(0 => 'c', 1 => 'd'); print_r(array_slice($input, 2, -1, true)); // array(2 => 'c', 1 => 'd');
运行步骤
处理参数:offset、length
移动指针到offset指向的位置
从offset开始,拷贝length个元素到返回数组
运行流程图如下
array_splice
array array_splice ( array &$input , int $offset [, int $length = 0 [, mixed $replacement = array() ]] )
删除input中从offset开始length个元素,如果有replacement参数的话用replacement数组替换删除掉的元素。
参数说明
array_splice函数中的offset和length参数跟array_slice函数中的用法一样。
replacement
如果这个参数设置了,那么函数将使用replacement数组来替换。
如果offset和length指定了没有任何元素需要移除,那么replacement会被插入到offset的位置。
如果replacement只有一个元素,可以不用array()去包着它。
<?php $input = array("red", "green", "blue", "yellow"); array_splice($input, 2); // $input变为 array("red", "green") $input = array("red", "green", "blue", "yellow"); array_splice($input, 1, -1); // $input变为 array("red", "yellow") $input = array("red", "green", "blue", "yellow"); array_splice($input, 1, count($input), "orange"); // $input变为 array("red", "orange") $input = array("red", "green", "blue", "yellow"); array_splice($input, -1, 1, array("black", "maroon")); // $input为 array("red", "green", // "blue", "black", "maroon") $input = array("red", "green", "blue", "yellow"); array_splice($input, 3, 0, "purple"); // $input为 array("red", "green", // "blue", "purple", "yellow");
源码解读
在array_splice中,有这么一段代码:
/* Don't create the array of removed elements if it's not going * to be used; e.g. only removing and/or replacing elements */ if (return_value_used) { // 如果有用到函数返回值则创建返回数组,否则不创建返回数组 int size = length; /* Clamp the offset.. */ if (offset > num_in) { offset = num_in; } else if (offset < 0 && (offset = (num_in + offset)) < 0) { offset = 0; } /* ..and the length */ if (length < 0) { size = num_in - offset + length; } else if (((unsigned long) offset + (unsigned long) length) > (unsigned) num_in) { size = num_in - offset; } /* Initialize return value */ array_init_size(return_value, size > 0 ? size : 0); rem_hash = &Z_ARRVAL_P(return_value); }
array_splice函数返回的是被删除的切片。这段代码的意思是,如果array_splice需要返回值,那么才创建返回数组,否则不创建,以免浪费空间。这也是一个编程小技巧,仅当需要的时候才返回。比如在函数中使用$result = array_splice(...),那么return_value_used就是true。
总结
到此本文结束,在平时编程中,应当像这两个函数实现时的做法一样,将最特殊的情况先处理掉,然后再继续,以免做了多余的判断;有需要保存新变量的时候才申请新的空间,不然会造成浪费。
以上就是PHP array_splice函数使用方法的内容,更多相关内容请关注PHP中文网(www.php.cn)!

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