Convert C++ code to PHP? - php

Question

I am trying to write a struct in php, i know there is no such thing in php, but at least get it working somehow...
C++:
// The struct
typedef struct data
{
char numbers[20];
char numbers2[50];
char number3[6];
char sometext[100];
}data_t;
data_t config;
char numbers[20] = "12345.12345";
char numbers3[6] = "12345";
char sometext[100] = "asdsadsad";
// Storing into struct
strcpy_s(config.numbers, numbers);
strcpy_s(config.numbers3, numbers3);
strcpy_s(config.sometext, sometext);
// Serializing struct to test.dat
ofstream output_file("test.dat", ios::binary);
output_file.write((char*)&config, sizeof(config));
output_file.close();
// Reading from it
ifstream input_file("test.dat", ios::binary);
input_file.read((char*)&master, sizeof(master));
cout << "NUMBERS : " << master.numbers << endl;
cout << "NUMBERS3 : " << master.numbers3 << endl;
cout << "SOMETEXT : " << master.sometext << endl;
cout << endl << endl;
Now storing with c++ in the struct, then reading it works just fine, but i want to store in that file trough php, then read it from c++, so i have:
PHP:
$data = Array();
$data['numbers'] = "12345.12345";
$data['numbers3'] = "12345";
$data['sometext'] = "abcdfghs";
$fp=fopen("test.dat","wb") or die("Stop! i kill you...");
foreach($data as $key => $value){
echo 'written:'.$value;
fwrite($fp,$value."\t");
}
Now what is happening is:
NUMBERS : 12345.12345 12345 abcdfghs
NUMBERS3 :
SOMETEXT :
So as you can see, it`s not good, also i noticed a difference when writing to file from c++ (contains binary data), while writing to file from php is just plain text.
Some help would be apreciated, many thanks!

Answer 1

Your C++ struct allocates 20 bytes for the numbers member. That means when you write it to the file, all 20 bytes are written, the writing doesn't just stop after writing 12345.12345. Your PHP code, on the other hand, writes exactly what is in $data['numbers'] and stops immediately (well, after adding a useless "\t"). The "binary data" you noticed in the file is just the garbage which happened to be in memory in those leftover bytes after 12345.12345. Same goes for the other fields.
Your PHP code does not write the string's terminating NULL to the file.
Your PHP code does not write the numbers2 member to the file.
You need to ensure the PHP code writes the terminating NULL, pads the output to the same size as the field has in the C++ struct, and outputs the fields in the same order as the C++ struct. You can use pack() for this:
<?php
$data = array();
$data['numbers'] = "12345.12345";
$data['numbers2'] = '';
$data['numbers3'] = "12345";
$data['sometext'] = "abcdfghs";
$packed = pack('a20a50a6a100', $data['numbers'], $data['numbers2'], $data['numbers3'], $data['sometext']);
$written = file_put_contents("test.dat", $packed);
if($written === false) {
throw new RuntimeException("Failed to write data to file!");
} else if($written !== strlen($packed)) {
throw new RuntimeException("Writing to file was not complete!");
}
Note: For maximum compatibility, you should read/write each struct member to the file individually in a consistent order on both sides. Otherwise you can have problems due to C++ field padding/alignment.