Using php, how to insert text without overwriting

问题:

I have:

<?php

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

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

fclose($file);

?>

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

回答1:

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?

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"]."\n");
}

fclose($file);

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, $new_content."\n".$old_content);

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:

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.

回答2:

A working example for inserting in the middle of a file stream without overwriting, and without having to load the whole thing into a variable/memory:

function finsert($handle, $string, $bufferSize = 16384) {
    $insertionPoint = ftell($handle);

    // Create a temp file to stream into
    $tempPath = tempnam(sys_get_temp_dir(), "file-chainer");
    $lastPartHandle = fopen($tempPath, "w+");

    // Read in everything from the insertion point and forward
    while (!feof($handle)) {
        fwrite($lastPartHandle, fread($handle, $bufferSize), $bufferSize);
    }

    // Rewind to the insertion point
    fseek($handle, $insertionPoint);

    // Rewind the temporary stream
    rewind($lastPartHandle);

    // Write back everything starting with the string to insert
    fwrite($handle, $string);
    while (!feof($lastPartHandle)) {
        fwrite($handle, fread($lastPartHandle, $bufferSize), $bufferSize);
    }

    // Close the last part handle and delete it
    fclose($lastPartHandle);
    unlink($tempPath);

    // Re-set pointer
    fseek($handle, $insertionPoint + strlen($string));
}

$handle = fopen("file.txt", "w+");
fwrite($handle, "foobar");
rewind($handle);
finsert($handle, "baz");

// File stream is now: bazfoobar

Composer lib for it can be found here

回答3:

You get the same opening the file for appending

<?php
$file=fopen(date("Y-m-d").".txt","a+") or exit("Unable to open file!");
if ($_POST["lastname"] <> "")
{
   fwrite($file,$_POST["lastname"]."\n");
}
fclose($file);
?>

回答4:

If you want to put your text at the beginning of the file, you'd have to read the file contents first like:

<?php

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

if ($_POST["lastname"] <> "")
{    
    $existingText = file_get_contents($file);
    fwrite($file, $existingText . $_POST["lastname"]."\n");
}

fclose($file);

?>