binary safe write on file with php to create a DBF file

问题

I need to split a big DBF file using php functions, this means that i have for example 1000 records, i have to create 2 files with 500 records each.

I do not have and dbase extension available nor i can install it so i have to work with basic php functions. Using basic fread function i'm able to correctly read and parse the file, but when i try to write a new dbf i have some problems.

As i have understood, the DBF file is structured in a 2 line file: the first line contains file info, header info and it's in binary. The second line contains the data and it's plain text. So i thought to simply write a new binary file replicating the first line and manually adding the first records in the first file, the other records in the other file.

That's the code i use to parse the file and it works nicely

    $fdbf = fopen($_FILES['userfile']['tmp_name'],'r');
    $fields = array();
    $buf = fread($fdbf,32);
    $header=unpack( "VRecordCount/vFirstRecord/vRecordLength", substr($buf,4,8));
    $goon = true;
    $unpackString='';
    while ($goon && !feof($fdbf)) { // read fields:
        $buf = fread($fdbf,32);
        if (substr($buf,0,1)==chr(13)) {$goon=false;} // end of field list
        else {
            $field=unpack( "a11fieldname/A1fieldtype/Voffset/Cfieldlen/Cfielddec", substr($buf,0,18));

            $unpackString.="A$field[fieldlen]$field[fieldname]/";
            array_push($fields, $field);
        }
    }
    fseek($fdbf, 0);
    $first_line = fread($fdbf, $header['FirstRecord']+1);

    fseek($fdbf, $header['FirstRecord']+1); // move back to the start of the first record (after the field definitions)

first_line is the variable the contains the header data, but when i try to write it in a new file something wrong happens and the row isn't written exactly as it was read. That's the code i use for writing:

$handle_log = fopen($new_filename, "wb");
fwrite($handle_log, $first_line, strlen($first_line) );
fwrite($handle_log, $string );
fclose($handle_log);

I've tried to add the b value to fopen mode parameter as suggested to open it in a binary way, i've also taken a suggestion to add exactly the length of the string to avoid the stripes of some characters but unsuccessfully since all the files written are not correctly in DBF format. What can i do to achieve my goal?

回答1:

As i have understood, the DBF file is structured in a 2 line file: the first line contains file info, header info and it's in binary. The second line contains the data and it's plain text.

Well, it's a bit more complicated than that.

See here for a full description of the dbf file format.

So it would be best if you could use a library to read and write the dbf files.

If you really need to do this yourself, here are the most important parts:

Dbf is a binary file format, so you have to read and write it as binary. For example the number of records is stored in a 32 bit integer, which can contain zero bytes.
You can't use string functions on that binary data. For example strlen() will scan the data up to the first null byte, which is present in that 32 bit integer, and will return the wrong value.
If you split the file (the records), you'll have to adjust the record count in the header.
When splitting the records keep in mind that each record is preceded by an extra byte, a space 0x20 if the record is not deleted, an asterisk 0x2A if the record is deleted. (for example, if you have 4 fields of 10 bytes, the length of each record will be 41) - that value is also available in the header: bytes 10-11 - 16-bit number - Number of bytes in the record. (Least significant byte first)
The file could end with the end-of-file marker 0x1A, so you'll have to check for that as well.

来源：https://stackoverflow.com/questions/50628785/binary-safe-write-on-file-with-php-to-create-a-dbf-file

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php

dbf