C/C++ Structure Byte Order Converter

Introduction

This script can read a C/C++ structure definition from the clipboard and generate byte reversing functions for the structure with ntoh or hton APIs.

Usage

Suppose we have a structure Foo:

struct Foo {
    unsigned short us;
    int i8 : 8;
    int i24 : 24;
    signed long sl[4];
    char c[12];
    long long ll24 : 24;
    signed int si8 : 8;
    short s;
};

Copy the structure definition to the clipboard and run the script. We can get two reversing functions:

void ReverseFooToLittleEndian(Foo *const data) {
    data->us = ntohs(data->us);
    *(int*)((unsigned char*)(&data->us) + sizeof(data->us) + 0) = ntohl(*(int*)((unsigned char*)(&data->us) + sizeof(data->us) + 0));
    for (size_t i = 0; i < sizeof(data->sl) / sizeof(data->sl[0]); i++) {
        data->sl[i] = ntohl(data->sl[i]);
    }
    *(long long*)((unsigned char*)(&data->c) + sizeof(data->c) + 0) = ntohll(*(long long*)((unsigned char*)(&data->c) + sizeof(data->c) + 0));
    *(signed int*)((unsigned char*)(&data->c) + sizeof(data->c) + 8) = ntohl(*(signed int*)((unsigned char*)(&data->c) + sizeof(data->c) + 8));
    data->s = ntohs(data->s);
}

void ReverseFooToBigEndian(Foo *const data) {
    data->us = htons(data->us);
    *(int*)((unsigned char*)(&data->us) + sizeof(data->us) + 0) = htonl(*(int*)((unsigned char*)(&data->us) + sizeof(data->us) + 0));
    for (size_t i = 0; i < sizeof(data->sl) / sizeof(data->sl[0]); i++) {
        data->sl[i] = htonl(data->sl[i]);
    }
    *(long long*)((unsigned char*)(&data->c) + sizeof(data->c) + 0) = htonll(*(long long*)((unsigned char*)(&data->c) + sizeof(data->c) + 0));
    *(signed int*)((unsigned char*)(&data->c) + sizeof(data->c) + 8) = htonl(*(signed int*)((unsigned char*)(&data->c) + sizeof(data->c) + 8));
    data->s = htons(data->s);
}

The output can be copied directly to the clipboard:

PS> .\Build-ByteReverseFunctions.ps1 | Set-Clipboard

Warnings

• The structure name can only be extracted from the struct statement.
• The script can only detect single-line comments (//).
• The following settings may differ from the script on some systems and compilers.
  • Endianness.
  • The sizes of fundamental C/C++ types.
  • The order of bit-fields.
  • Field alignment.

License

Distributed under the MIT License. See LICENSE for more information.