Is it possible to update my game without breaking existing save files from older versions?

Question

Ryan McCombe · Accepted Answer

This is a critical consideration for any game that will receive updates. The solution involves implementing a versioning system for your save files. Here's how it typically works:

First, include a version number in your save file format. This should be one of the first pieces of data you write:

1#include <fstream>
2#include <string>
3
4struct GameSave {
5  int Version{1}; // Current save format version
6  std::string PlayerName;
7  int Score;
8  // Other game data...
9};
10
11void SaveGame(const GameSave& Save) {
12  std::ofstream File{
13    "save.dat", std::ios::binary};
14  File.write(
15    reinterpret_cast<const char*>(
16      &Save. Version),
17    sizeof(Save.Version)
18  );
19  // Write remaining data...
20}

When loading, first read the version number and handle different versions appropriately:

1GameSave LoadGame() {
2  GameSave Save;
3  std::ifstream File{
4    "save.dat", std::ios::binary};
5
6  // Read version first
7  int FileVersion{};
8  File.read(
9    reinterpret_cast<char*>(&FileVersion),
10    sizeof(FileVersion));
11
12  if (FileVersion == 1) {
13    // Handle version 1 format
14  } else if (FileVersion == 2) {
15    // Handle version 2 format
16  }
17
18  return Save;
19}

When you update your game and need to change the save format, increment the version number and add code to convert old saves to the new format. For example, if version 2 adds a new Level field:

1GameSave ConvertSaveV1ToV2(
2  const GameSave& OldSave
3) {
4  GameSave NewSave;
5  NewSave.Version = 2;
6  NewSave.PlayerName = OldSave.PlayerName;
7  NewSave.Score = OldSave.Score;
8  
9  // Set default for new field
10  NewSave.Level = 1;
11  return NewSave;
12}

The key is to never remove old loading code - always maintain the ability to load all previous versions of your save format. This ensures players can continue their games even after updates.

Working with Data

Managing Save File Versions

Working with Data

Game Development with SDL2

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