Read C++ QString binary data with PHP - php

Question

I have to read a binary file written by a C++ app using Qt framework. Data is structured from a C struct as described below. Chars are written from a QString pointer in the C++ app.
struct panelSystem{
char ipAddress[16];
char netMask[16];
char gateway[16];
char paddingBytes[128];
};
I tried using the following PHP code to read the multibyte char values :
// Where: $length is a defined number (16 or 128 in this case)
// $data is a binary string read from the binary file
$var = substr($data, $currentOffset, $length);
$currentOffset += $length; // Increment offset by X bytes
$var = trim(str_replace("\0", "\n", $var));
$var = unpack("C*", $var);
$char = '';
foreach ($var as $letter) {
$char .= chr($letter);
}
$var = $char;
Unfortunately the result includes null (\0) and/or irrelevant characters before and after the desired char.
Is there a way to interpret or convert those char from QString multibyte array to PHP standard string (without modifying the original input) ?
Thank you.

Answer 1

A QString will be written to the binary with (at least) a length value and the character data. You also will need to take into account how the string is formatted. It might be in unicode utf-16, in which case, simple chars will have each character padded with zeros. Where the zeros go will depend upon what endian-ness the file is written in, though IIRC Qt will always store files in one particular endian-ness, regardless of the platform so that binaries are cross platform.
Have a look in the Qt source code to see how strings are written. Maybe also take a look at the binary file in a hex editor.
If your binary file only ever contains the struct, and you don't have a problem with the binary format being fixed, then you may find things far easier to write the file using raw IO:
struct panelSystem{
char ipAddress[16];
char netMask[16];
char gateway[16];
char paddingBytes[128];
void write(QDataStream& ds) {
ds.writeRawData(ipAddress, sizeof(ipAddress));
ds.writeRawData(netMask, sizeof(netMask));
ds.writeRawData(gateway, sizeof(gateway));
ds.writeRawData(paddingBytes, sizeof(paddingBytes));
}
};
//...
panelSystem p;
GetPanelSystemData(&p);
QFile file("c:\\work\\test\\testbin.bin");
if (file.open(QIODevice::Truncate | QIODevice::WriteOnly)) {
QDataStream ds(&file);
p.write(ds);
}
file.close();
I would recommend at least adding a version number/header to the start binary file to prevent painting yourself into a corner.