Host byte, network byte, observe directly through debugger

Throughout the history of computer development, there has been no unified standard for data storage. There are two commonly used rules for byte arrangement. For example, if the low-order bits of a multi-digit number are placed at smaller addresses and the high-order bits are placed at larger addresses, it is referred to as little-endian; conversely, it is called big-endian. In network applications, byte order is a factor that must be considered because different types of machines may adopt different standards, so they are all converted according to the network standard. According to reading habits, big-endian byte order is more consistent with the left-to-right reading order.

Processor Architecture

Processors such as x86, MOS Technology 6502, Z80, VAX, and PDP-11 use little-endian byte order.
Processors like Motorola 6800, Motorola 68000, PowerPC 970 use big-endian byte order.
The byte order of processors such as ARM, PowerPC (excluding PowerPC 970), DEC Alpha, SPARC V9, MIPS, PA-RISC and IA64 is configurable.

Network Byte Order

Network transmission generally uses big-endian byte order, also known as network byte order or network order. The IP protocol defines big-endian as the network byte order.

The Berkeley sockets API defined a set of conversion functions to convert 16 and 32-bit integers between network byte order and host byte order.

#include <arpa/inet.h>

uint32_t htonl(uint32_t hostlong); // Converts a uint32_t from host byte order to network byte order
uint16_t htons(uint16_t hostshort); // Converts a uint16_t from host byte order to network byte order
uint32_t ntohl(uint32_t netlong); // Converts a uint32_t from network byte order to host byte order
uint16_t ntohs(uint16_t netshort); // Converts a uint16_t from network byte order to host byte order

If using asio as the networking library, its internal namespace provides cross-platform adaptation functions with different names:

boost::asio::detail::socket_ops::network_to_host_long
boost::asio::detail::socket_ops::network_to_host_short
boost::asio::detail::socket_ops::host_to_network_long
boost::asio::detail::socket_ops::host_to_network_short

Visual Studio Debugger

In debugging mode, select the Debug menu, Window, and checkmark the Memory window. Within Visual Studio, you can directly view data in memory using the debugger, as shown in the following image:

Debugger Menu

Ways to View Memory

The window directly outputs &variable name and jumps to the corresponding variable address.
If the variable is originally a pointer, double-click on the variable to select it and drag it to the memory window to display the content at the corresponding address.
If the variable is not a pointer, add it to the calculation window to obtain its address, then manually copy it to the memory window.

Let’s illustrate with an example

Receive a data segment, stored in the buffer object, convert network byte order to host byte order, resulting in body_length being 30. The server allocates four bytes for transmitting this data.

bool NetworkMessage::decode_header()
{
    // Network byte order to host byte order
    body_length_ = boost::asio::detail::socket_ops::network_to_host_long(*(int *)buffer_.data());
    return auto_reserve(body_length_);
}

Big-endian byte order: When observing the buffer_ content in memory, buffer_

Little-endian byte order: When observing the content of body_length_ in memory,