php 一行行读取文本文件

例子

/**
 *
 * Read a line number from a file
 *
 * @param    string    $file    The path to the file
 * @param    int    $line_num    The line number to read
 * @param    string    $delimiter    The character that delimits lines
 * @return    string    The line that is read
 *
 */
function readLine($file, $line_num, $delimiter=" ")
{
    /*** set the counter to one ***/
    $i = 1;

    /*** open the file for reading ***/
    $fp = fopen( $file, 'r' );

    /*** loop over the file pointer ***/
    while ( !feof ( $fp) )
    {
        /*** read the line into a buffer ***/
        $buffer = stream_get_line( $fp, 1024, $delimiter );
        /*** if we are at the right line number ***/
        if( $i == $line_num )
        {
            /*** return the line that is currently in the buffer ***/
            return $buffer;
        }
        /*** increment the line counter ***/
        $i++;
        /*** clear the buffer ***/
        $buffer = '';
    }
    return false;
}
?>

Example Usage

/*** make sure the file exists ***/
$file = 'my_file.txt';

if( file_exists( $file ) && is_readable( $file ) )
{
    echo readLine($file, 6);
}
else
{
    echo "Cannot read from $file";
}
?>

This method of iterating over the file and seeking to the line number works well and is memory efficient, but it would be nice to have PHP do the work for us. PHP provides the SPL File Object which will do exactly what is required.

/*** the file to read ***/
$file = 'foo.txt';

       
/**
 *
 * Read a line number from a file
 *
 * @param    string    $file    The path to the file
 * @param    int    $line_num    The line number to read
 * @return    string    The line that is read
 *
 */
function readLine( $file, $line_number )
{
        /*** read the file into the iterator ***/
        $file_obj = new SplFileObject( $file );

        /*** seek to the line number ***/
        $file_obj->seek( $line_number );

        /*** return the current line ***/
        return $file_obj->current();
}

echo readLine( $file, 345678 );

?>