# SplFileObject::key

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

SplFileObject::key — Get line number

### 说明

public SplFileObject::key(): int

Gets the current line number.

> 注意:

> This number may not reflect the actual line number in the file if SplFileObject::setMaxLineLen() is used to read fixed lengths of the file.

### 参数

此函数没有参数。

### 返回值

Returns the current line number.

### 示例

示例 #1 SplFileObject::key() example

`<?php
$file = new SplFileObject("lipsum.txt");
foreach ($file as $line) {
echo $file->key() . ". " . $line;
}
?>`

以上示例的输出类似于：

    0. Lorem ipsum dolor sit amet, consectetur adipiscing elit.
    1. Duis nec sapien felis, ac sodales nisl.
    2. Lorem ipsum dolor sit amet, consectetur adipiscing elit.

示例 #2 SplFileObject::key() example with SplFileObject::setMaxLineLen()

`<?php
$file = new SplFileObject("lipsum.txt");
$file->setMaxLineLen(20);
foreach ($file as $line) {
echo $file->key() . ". " . $line . "\n";
}
?>`

以上示例的输出类似于：

    0. Lorem ipsum dolor s
    1. it amet, consectetu
    2. r adipiscing elit.
    3.

    4. Duis nec sapien fel
    5. is, ac sodales nisl
    6. .

    7. Lorem ipsum dolor s
    8. it amet, consectetu
    9. r adipiscing elit.

### 参见

- SplFileObject::current() - Retrieve current line of file
- SplFileObject::seek() - Seek to specified line
- SplFileObject::next() - Read next line
- SplFileObject::rewind() - Rewind the file to the first line
- SplFileObject::valid() - Not at EOF

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