使用php，如何插入文本而不覆盖文本文件的开头

问题描述

我有:

<?php

$file=fopen(date("Y-m-d").".txt","r+") or exit("Unable to open file!");

if ($_POST["lastname"] <> "")
{
   fwrite($file,$_POST["lastname"]."
");
}

fclose($file);

?>

但它会覆盖文件的开头.如何让它插入?

but it overwrites the beginning of the file. How do I make it insert?

推荐答案

我不完全确定您的问题 - 您是要写入数据并且不让它覆盖现有文件的开头，还是写入新文件数据到现有文件的开头，在其后保留现有内容?

I'm not entirely sure of your question - do you want to write data and not have it over-write the beginning of an existing file, or write new data to the start of an existing file, keeping the existing content after it?

要插入文本而不覆盖文件的开头，您必须打开它以进行附加 (a+ 而不是 r+)

To insert text without over-writing the beginning of the file, you'll have to open it for appending (a+ rather than r+)

$file=fopen(date("Y-m-d").".txt","a+") or exit("Unable to open file!");

if ($_POST["lastname"] <> "")
{
   fwrite($file,$_POST["lastname"]."
");
}

fclose($file);

如果您尝试写入文件的开头，则必须读入文件内容(请参阅 file_get_contents)，然后将新字符串和文件内容写入输出文件.

If you're trying to write to the start of the file, you'll have to read in the file contents (see file_get_contents) first, then write your new string followed by file contents to the output file.

$old_content = file_get_contents($file);
fwrite($file, $new_content."
".$old_content);

上述方法适用于小文件，但您可能会在尝试使用 file_get_conents 读取大文件时遇到内存限制.在这种情况下，请考虑使用 rewind($file)，它设置文件文件流开头句柄的位置指示器.注意使用rewind()时，不要用a(或a+)选项打开文件，如:

The above approach will work with small files, but you may run into memory limits trying to read a large file in using file_get_conents. In this case, consider using rewind($file), which sets the file position indicator for handle to the beginning of the file stream. Note when using rewind(), not to open the file with the a (or a+) options, as:

如果您以追加(a"或a+")模式打开文件，则无论文件位置如何，您写入文件的任何数据都将始终被追加.

If you have opened the file in append ("a" or "a+") mode, any data you write to the file will always be appended, regardless of the file position.

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