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Using the C++ Host SDK

Check your installation

Please be sure you've installed Extism before continuing with this guide.

1. Install the C++ library​

Install via git:

git submodule add https://github.com/extism/extism extism
Choose a version

It is recommended that you lock this submodule to a release tag.

First edit .gitmodules to point to the tag

[submodule "extism"]
    path = extism
    url = https://github.com/extism/extism
    tag = v0.1.0

N.B.: See the Extism releases page for available versions

Then update:

git submodule foreach --recursive 'git fetch --tags'
git submodule update --init --recursive --remote
git commit -am 'Lock extism version to v0.1.0'

2. Include the library and use the APIs​

Count Vowels Plugin

code.wasm in this example is our example plugin that counts vowels. If you want to run this, download it first and set the path:

curl https://raw.githubusercontent.com/extism/extism/main/wasm/code.wasm > code.wasm
main.cpp
#include "extism/cpp/extism.hpp"


#include <cstring>
#include <fstream>
#include <iostream>

using namespace extism;

std::vector<uint8_t> read(const char *filename) {
  std::ifstream file(filename, std::ios::binary);
  return std::vector<uint8_t>((std::istreambuf_iterator<char>(file)),
                              std::istreambuf_iterator<char>());
}

int main(int argc, char *argv[]) {
  auto wasm = read("../wasm/code.wasm");
  Context context = Context();

  Plugin plugin = context.plugin(wasm);

  const char *input = argc > 1 ? argv[1] : "this is a test";
  ExtismSize length = strlen(input);

  extism::Buffer output = plugin.call("count_vowels", (uint8_t *)input, length);
  std::cout << (char *)output.data << std::endl;
  return 0;
}

Need help?​

If you've encountered a bug or think something is missing, please open an issue on the Extism GitHub repository.

There is an active community on Discord where the project maintainers and users can help you. Come hang out!