Cross-Language Binary Data Transfer: Writing in C++ and Reading in Python
Published: 2023-06-12 14:20:53

In today's world of software development, multiple programming languages are used to create complex systems. Each programming language has its own advantages and disadvantages, and developers prefer to use the language of their choice. However, transferring data between different programming languages can be challenging, especially when it comes to binary data.

Binary data transfer involves sending data in its raw and unprocessed form, which can be difficult to interpret by another programming language. Cross-language binary data transfer plays a crucial role in enabling data exchange between different programming languages, making it possible to create complex systems that are not limited by language barriers. This makes cross-language binary data transfer an essential tool for developers who need to work with multiple programming languages.

In this article, we'll provide sample code to illustrate the process of writing binary data in C++ and reading it in Python using the Boost C++ libraries and the struct Python module. We hope that this article will provide valuable insights for developers who need to transfer binary data between programming languages.

## Understanding Binary Data Transfer
Binary data transfer refers to the process of transmitting data in its raw binary format from one system to another. This form of data transfer is more efficient than other forms of data transfer, such as textual transfer, as binary data can be packed tightly and sent in a single transmission.

When data is transferred in binary format, it is important to ensure that both the sending and receiving systems have a clear understanding of the binary format being used. Any differences in the binary format can result in data corruption, rendering the transferred data unusable.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/2ycdrkebq5h17lksmnms.png)


Binary data transfer involves encoding data in a machine-readable format that can be easily read and processed by computer programs. One of the main advantages of binary data transfer is speed since it eliminates the need for data translation, parsing, and conversion. Binary data is also compact, which means it takes up less space than text-based data, making it ideal for data transfer over networks.

However, binary data transfer has some disadvantages too. Firstly, it is not human-readable, which makes debugging and troubleshooting difficult. The encoding and decoding process can also be complex and prone to errors, which can lead to data corruption. Finally, binary data transfer is platform-dependent, which means that it may not be compatible across different hardware and software platforms.

## Writing Binary Data in C++
To perform cross-language binary data transfer between C++ and Python, we need to set up the development environment first. In this case, we will be using Lightly IDE as our[online C++ compiler](https://www.lightly-dev.com/cpp/). The Lightly IDE has all the necessary dependencies preconfigured to support both C++ and Python languages. It provides syntax highlighting, code snippets, code completion and debugging tools for both C++ and Python.

With the development environment set up, we can now start writing our code to perform cross-language binary data transfer.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/exq7v2nbuypfs27v50pw.png)


### Creating data structure for both C++ and Python
Before sending binary data from C++ to Python, it is important to define a structure that both languages can understand.

One option is to use a struct in C++ that matches the layout of the corresponding Python data structure. Here's an example:

```cpp
// Example of a C++ struct matching the layout of a Python data structure

#include <iostream>
#include <string>

struct Person {
  std::string name;
  int age;
};

int main() {
  // Creating an instance of the Person struct
  Person person1;
  person1.name = "John";
  person1.age = 30;

  // Accessing and printing the values
  std::cout << "Name: " << person1.name << std::endl;
  std::cout << "Age: " << person1.age << std::endl;

  return 0;
}
```

In this example, the C++ struct Person has the same fields as the Python class in the previous example (name and age). The struct is defined with the same field types (std::string and int), and we create an instance of the struct named person1. We assign values to its fields using the dot notation (person1.name and person1.age), and then we print the values using std::cout.

Another option is to use a library like Protocol Buffers or MsgPack to define a language-agnostic data structure. These libraries provide serialization and deserialization capabilities, allowing you to define data structures that can be easily serialized into binary format and then deserialized in another language.

Here's an example of using Protocol Buffers to define a data structure that can be transferred between C++ and Python:

Define the data structure using Protocol Buffers syntax in a .proto file. Let's assume we have a person.proto file:
```cpp
syntax = "proto3";

message Person {
  string name = 1;
  int32 age = 2;
}
```

Compile the .proto file using the Protocol Buffers compiler to generate language-specific code. For C++, you would use the protoc compiler with the --cpp_out option:
```cpp
$ protoc --cpp_out=. person.proto
```

This will generate the C++ header and source files (person.pb.h and person.pb.cc) for the defined data structure.

Use the generated C++ code to create a Person instance and serialize it into binary format:
```cpp
#include <iostream>
#include "person.pb.h"

int main() {
  // Creating a Person instance
  Person person;
  person.set_name("John");
  person.set_age(30);

  // Serializing the Person instance to binary format
  std::string serialized_data = person.SerializeAsString();

  // Transfer the serialized_data to Python...

  return 0;
}
```

On the Python side, install the Protocol Buffers library (protobuf package) using pip:
```
$ pip install protobuf
```

Use the generated Python code (also generated by the Protocol Buffers compiler) to deserialize the binary data:
```python
from person_pb2 import Person

# Assuming serialized_data is the binary data transferred from C++
person = Person()
person.ParseFromString(serialized_data)

# Accessing and printing the values
print("Name:", person.name)
print("Age:", person.age)
```

By using Protocol Buffers, you define a data structure in a language-agnostic way, generate language-specific code for both C++ and Python, and serialize/deserialize the data using the generated code. This allows for easy and efficient binary data transfer between the two languages. The steps above outline a basic workflow, but you may need to refer to the documentation of Protocol Buffers or MessagePack for more detailed information on installation, compilation, and usage.

Once a data structure is defined, the C++ code can populate it with data and serialize it to a binary format that can be sent to Python. On the Python side, the binary data can be deserialized and the data structure can be accessed to retrieve the data. Overall, creating a shared data structure is an important step in enabling cross-language binary data transfer.

### Converting data to binary format in C++
When working with binary data, it is important to be able to write this data to a file so that it can be stored and later read in by another program.

To do this in C++, first we need to convert our data into binary format, which can be done using the reinterpret_cast operator to reinterpret the data as a char* pointer. This allows us to write the data to a binary file using the std::ofstream class and its write() function.

Here's an example that demonstrates this process:

```cpp
#include <iostream>
#include <vector>

int main() {
  // Data to convert into binary format
  int intValue = 42;
  double doubleValue = 3.14;

  // Reinterpret the data as char* pointer
  char* dataPtr = reinterpret_cast<char*>(&intValue);

  // Determine the size of the data
  size_t dataSize = sizeof(intValue);

  // Create a vector to hold the binary data
  std::vector<char> binaryData(dataPtr, dataPtr + dataSize);

  // Print the binary data
  for (char byte : binaryData) {
    std::cout << static_cast<int>(byte) << " ";
  }
  std::cout << std::endl;

  return 0;
}
```

In this example, we have an int variable intValue and a double variable doubleValue that we want to convert into binary format. We use reinterpret_cast to reinterpret the addresses of the variables as char* pointers (dataPtr).

Next, we determine the size of the data by using sizeof() on the variables. In this case, we use sizeof(intValue) to get the size of the intValue variable.

Then, we create a std::vector<char> named binaryData and initialize it with the dataPtr and dataSize. This creates a vector that contains the bytes of the data.

Finally, we iterate over the binaryData vector and print each byte as an integer value.

### Writing data to a file in C++
When writing data to a file, it is important to consider how the data will be read by another program. In cross-language binary data transfer, it is necessary to ensure that the data is written in a format that can be read by the receiving program.

For instance, when writing data in C++, it is important to specify the byte ordering and data size to ensure that the data can be correctly interpreted by the Python program that will read it. 

```cpp
#include <iostream>
#include <fstream>
#include <vector>

struct Person {
  char name[20];
  int age;
};

int main() {
  std::vector<Person> persons = {
    { "John", 30 },
    { "Jane", 25 },
    { "Tom", 40 }
  };

  std::ofstream file("data.bin", std::ios::binary);

  if (file.is_open()) {
    for (const auto& person : persons) {
      // Write name
      file.write(reinterpret_cast<const char*>(person.name), sizeof(person.name));

      // Convert age to network byte order (big-endian)
      int age = htonl(person.age);
      file.write(reinterpret_cast<const char*>(&age), sizeof(age));
    }

    file.close();
    std::cout << "Data written to file." << std::endl;
  }
  else {
    std::cout << "Unable to open the file." << std::endl;
  }

  return 0;
}
```

In this example, we have a struct Person with two fields: name (a character array) and age (an integer). We define a vector of Person instances representing the data to be written.

To ensure cross-language compatibility, we open the file in binary mode (std::ios::binary) when creating the std::ofstream object.

Inside the loop, we write the name field as a character array using file.write(). Since the name field has a fixed size of 20 characters, we write exactly sizeof(person.name) bytes.

For the age field, we convert it to network byte order (big-endian) using the htonl() function. This ensures that the data will be interpreted correctly by the Python program, regardless of the byte ordering on different systems. We then write the age field using file.write().

Finally, we close the file and display a success message if the file was opened successfully or an error message if there was an issue opening the file.

Note that when reading this binary data in Python, you will need to consider the same byte ordering and data size considerations. You can use appropriate functions and libraries in Python, such as struct or numpy, to handle the conversion and interpretation of the binary data.

### Best practices for writing binary files in C++
When writing binary files in C++, there are some best practices that can help ensure data integrity, portability, and readability. Here are some tips to follow:

1. Use fixed-size integer types (such as uint32_t or int16_t) instead of the standard integer types to ensure consistent byte sizes across different systems.
2. Always write binary data in little-endian byte order, which is the most common byte order for most computer architectures.
3. Use structs to organize related data fields and make it easier to read and write binary data.
4. Always check for errors when writing binary data and handle them appropriately.
5. Avoid padding and alignment issues by using the pragma pack(1) directive to ensure that the struct members are packed tightly without any extra padding.
6. Use descriptive and consistent field and variable names to make the binary file easier to read and understand.

By following these best practices, you can ensure that your binary files are well-structured, cross-platform compatible and easy to maintain.

## Reading Binary Data files in Python
To begin with, you will need to have a C++ compiler and a Python interpreter installed on your system. For C++, we recommend using GCC or Clang. You can also use the online Python compiler built into Lightly IDE to comple your task. You will also need to install the Boost C++ libraries, which provide efficient and reliable cross-platform support for a wide range of tasks.

To install the Boost C++ library, you can follow these general steps:
1. Download the Boost library from the official website: https://www.boost.org/users/download/.
2. Extract the downloaded archive file.
3. Open a terminal or command prompt and navigate to the extracted Boost library directory.
4. Run the bootstrap script to configure the Boost installation:
```
./bootstrap.sh

or

bootstrap.bat
```
This script generates the necessary build files and sets up the Boost.Build system.

5. Build and install the Boost library by running the following command:
./b2 install
This command will build the Boost libraries and install them on your system. Note that this step may require administrative privileges on your system.

Wait for the installation process to complete. It may take some time, as Boost is a large library with many components. After the installation completes, you should have the Boost library installed on your system.

To facilitate the communication between the C++ and Python programs, we will use Google's Protocol Buffers, a language-agnostic binary serialization format that can be used to store and exchange data between different systems. To use Protocol Buffers in C++, you will need to install the protobuf compiler and runtime libraries. For Python, you can install the protobuf package using pip.

To install the Protocol Buffers (protobuf) compiler and runtime libraries, you can follow these general steps:

Linux: You can typically install protobuf using your distribution's package manager. For example, on Ubuntu, you can use the following command:
```shell
sudo apt-get install protobuf-compiler libprotobuf-dev
```

macOS: You can use Homebrew to install protobuf. Open a terminal and run the following command:
```shell
brew install protobuf
```

Windows: Download the precompiled binaries for protobuf from the official protobuf releases page (https://github.com/protocolbuffers/protobuf/releases). Choose the appropriate package for your Windows version and architecture (32-bit or 64-bit). Extract the downloaded archive and add the bin directory to your system's PATH environment variable.

Verify the installation by running the following commands in your terminal or command prompt:
```shell
protoc --version
```
This command should display the version number of the installed protobuf compiler.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/c8sejfdmrl1nfqg1x06y.png)


Additionally, you may want to install protobuf runtime libraries for the programming language you intend to use. For example, you'll need to install the protobuf package using pip, the Python package manager:

```shell
pip install protobuf
```

This command installs the protobuf runtime libraries for Python. Once you have these tools installed, you can start writing your C++ and Python code, and use Protocol Buffers to transfer binary data between them.

### Opening a Binary File in Python
Binary data is a sequence of bits and bytes that represent non-textual information, such as images, audio, compressed files, and more. In Python, reading binary data from a file is straightforward.

First, you need to open the file in binary mode by specifying the "rb" flag. 
```python
with open("data.bin", "rb") as file:
    # Perform operations on the opened file
    data = file.read()
    # Additional processing or analysis
```

In the above code, the open() function is used to open the file named "data.bin" in binary mode. The "rb" mode parameter specifies that the file should be opened in binary read mode.

The file is then accessed within a with statement, which ensures that the file is automatically closed after the block of code executes, even if an exception occurs. Inside the block, you can perform operations on the file. For example, the file.read() method is used to read the entire contents of the file as binary data and store it in the data variable.

You can then perform additional processing or analysis on the data variable as needed. Remember to replace "data.bin" with the actual file path and name you want to open.

When dealing with binary files, it is important to specify the mode in which the file should be opened. In Python, we can use the built-in open() function with the mode rb to open a file in binary mode for reading. If we want to write to a binary file, we can open the file in binary mode for writing using the mode wb.

Once you have the bytes object, you can process it as needed. For example, you can decode it into a string, extract specific parts, or convert it into a NumPy array. Overall, reading binary data in Python is a fundamental task that can enable you to work with a variety of file formats and data types.

### Converting binary data to Python data types
After receiving binary data from a C++ program, the next step is to convert it into Python data types. This can be done using the struct module in Python. The struct module provides functions for packing and unpacking binary data. The unpack function can be used to convert binary data into a tuple of Python objects.

The format string used in the unpack function should match the format string used in the C++ program to pack the data. Once the data is unpacked, it can be converted into the appropriate Python data types. For example, if the binary data represents an integer, the struct.unpack function will return a tuple containing a single integer value.

Here's an example that demonstrates how to use the struct module in Python to convert binary data received from a C++ program into Python data types:

```python
import struct

# Assuming 'received_data' is the binary data received from the C++ program
received_data = b'\x00\x00\x00\x1F'

# Define the format string to match the format used in the C++ program
format_string = "i"  # Assuming it represents a single integer value

# Unpack the binary data using the format string
unpacked_data = struct.unpack(format_string, received_data)

# Extract the unpacked value
integer_value = unpacked_data[0]

# Print the extracted value
print("Received integer value:", integer_value)
```

In this example, we start with the received_data variable, which represents the binary data received from the C++ program. The format_string is defined to match the format used in the C++ program, in this case, a single integer ("i").

Using the struct.unpack function, we unpack the binary data using the format string, which returns a tuple of unpacked values. Since we are expecting a single integer value, we extract it by accessing the first element of the unpacked_data tuple.

Finally, we print the extracted integer value to verify that the conversion from binary data to Python data type was successful. Note that you may need to adjust the format string and the extraction logic based on the specific data format used in your C++ program.

Remember to replace received_data with the actual binary data received from the C++ program, and modify the format_string to match the format used in your C++ program.

## Read Binary File in Python Written in C++ from Vector
To read binary data in Python that was written from a C++ program using a vector, you can follow these steps:

In the C++ program, use file I/O operations to open a file in binary mode and write the binary data from the vector.

```cpp 
#include <iostream>
#include <fstream>
#include <vector>

int main() {
  std::vector<int> data = {10, 20, 30, 40, 50};

  std::ofstream file("data.bin", std::ios::binary);
  if (file.is_open()) {
    file.write(reinterpret_cast<const char*>(data.data()), data.size() * sizeof(int));
    file.close();
    std::cout << "Binary data written to file." << std::endl;
  } else {
    std::cout << "Unable to open the file." << std::endl;
  }

  return 0;
}
```

In this C++ example, a vector data of integers is created and initialized. The file "data.bin" is opened in binary mode using std::ofstream. The binary data from the vector is written to the file using file.write(), specifying the starting address of the vector's data and the total number of bytes to write.

In the Python program, open the binary file using open() in binary mode, read the binary data, and interpret it.

```python
with open("data.bin", "rb") as file:
    binary_data = file.read()

# Interpret the binary data in Python as per your requirements
# For example, assuming the data contains integers:
import struct
integers = struct.unpack("i" * (len(binary_data) // 4), binary_data)
print("Integers:", integers)
```

In this Python example, the binary file "data.bin" is opened using open() with the "rb" flag to specify binary mode. The entire binary data is read using file.read() and stored in the binary_data variable.

The struct.unpack() function from the struct module is then used to interpret the binary data as integers. The format string "i" * (len(binary_data) // 4) specifies the format of the data as integers. The resulting unpacked integers are stored in the integers variable.

You can adapt the interpretation of the binary data based on the specific format and requirements of your data.

## Best practices for cross-language binary data transfer
Cross-language binary data transfer can be a challenging task, as it requires communication between different programming languages and may involve differences in data types and byte order. Here are some best practices to consider when transferring binary data between programming languages:

- Use a well-defined binary format, such as Protocol Buffers or Apache Avro, to ensure compatibility between different languages.
- Always specify the byte order, especially when transferring data between platforms with different endianness.
- Avoid using language-specific data types and instead use fixed-width types, such as int32_t or uint64_t.
- Use libraries or frameworks that support binary data transfer, such as Boost Serialization or Google's FlatBuffers.
- Consider using textual data formats, such as JSON or XML, when possible, as they are more human-readable and can be easily parsed by different programming languages. However, they may not be as efficient as binary formats for large data sets.

## Learning C++ and Python with Lightly IDE
Learning a new programming language might be intimidating if you're just starting out. Lightly IDE, however, makes learning Python simple and convenient for everybody. [Lightly IDE](https://www.lightly-dev.com/) was made so that even complete novices may get started writing code.

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Lightly IDE's intuitive design is one of its many strong points. If you've never written any code before, don't worry; the interface is straightforward. You may quickly get started with programming with our [online Python compiler](https://www.lightly-dev.com/python/) and [online C++ compiler](https://www.lightly-dev.com/cpp/) in only a few clicks.

The best part of Lightly IDE is that it is cloud-based, so your code and projects are always accessible from any device with an internet connection. You can keep studying and coding regardless of where you are at any given moment.

Lightly IDE is a great place to start if you're interested in learning programming. Learn and collaborate with other learners and developers on your projects and receive comments on your code now.

[Cross-Language Binary Data Transfer with C++ and Python](https://www.lightly-dev.com/blog/read-in-python-cpp-write-binary-file-from-vector/)