PHP读取和修改大文件的某行内容
最近碰到一个比较有趣的问题,就是修改某个文件的某一行字符,不过文件太大,file()直接读取是不可能的,我使用fgets来跳转到指定行,并用fwrite修改某个字符串:
$fp = fopen(d:/file.txt, r+);
if ($fp) {
$i = 1;
while (!feof($fp)) {
//修改第二行数据
if ($i == 2) {
fseek($fp, 2, SEEK_CUR);
fwrite($fp, #);
break;
}
fgets($fp);
$i++;
}
fclose($fp);
}
这里需要注意的是fgets获取到一行后,文件指针指向行尾(也就是下一行开头),所以fwrite操作的是fgets后的下一行开头,至于从该行的第几个字符开始写,可以使用fseek函数来移动文件指针。另外一个需要注意的是,这里fwrite写入是执行替换操作,而不是插入操作,所以指针后面的字符会一个个被替换掉。至于怎么插入我就没研究了。估计很困难。为了效率可能只能写入另外一个临时文件了,不知道有没有其他更好的方法。
另外今天还看到了使用SPL进行操作的方法:
$fp = new SplFileObject(d:/file.txt, r+);
//转到第二行, seek方法参数从0开始计数, 经我测试指针指向行尾了, 所以修改的是第三行
$fp->seek(1);
//获取当前行内容(第二行)
$line = $fp->current();
//下面是对第三行的操作
$fp->fseek(2, SEEK_CUR);
$fp->fwrite(#);
SplFileObject提供的方法比基本的文件操作函数更丰富一些,包括采用key/value方法遍历文件行等。SPL应该是PHP5增加进去的吧,还有其他很多很有用的对象。包括数组、文件目录操作、异常处理、一些基本类型操作等,这些功能还在陆续增加,可以通过继承SPL扩展这些方法让我们处理底层的操作更方便。

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