Crow/docs/getting_started/your_first_application.md

This page shows how you can get started with a simple hello world application.

1. Include

Starting with an empty main.cpp file, first add #!cpp #include "crow.h" or #!cpp #include "crow_all.h" if you're using the single header file.

!!! note

If you are using version v0.3, then you have to put `#!cpp #define CROW_MAIN` at the top of one and only one source file.

2. App declaration

Next Create a main() and declare a #!cpp crow::SimpleApp inside, your code should look like this

int main()
{
    crow::SimpleApp app;
}

The App (or SimpleApp) class organizes all the different parts of Crow and provides the developer (you) a simple interface to interact with these parts. For more information, please go here.

3. Adding routes

Once you have your app, the next step is to add routes (or endpoints). You can do so with the CROW_ROUTE macro.

CROW_ROUTE(app, "/")([](){
    return "Hello world";
});

For more details on routes, please go here.

4. Running the app

Once you're happy with how you defined all your routes, you're going to want to instruct Crow to run your app. This is done using the run() method.

app.port(18080).multithreaded().run();

Please note that the port() and multithreaded() methods aren't needed, Though not using port() will cause the default port (80) to be used.

Putting it all together

Once you've followed all the steps above, your code should look similar to this

#include "crow.h"
//#include "crow_all.h"

int main()
{
    crow::SimpleApp app; //define your crow application

    //define your endpoint at the root directory
    CROW_ROUTE(app, "/")([](){
        return "Hello world";
    });

    //set the port, set the app to run on multiple threads, and run the app
    app.port(18080).multithreaded().run();
}

For the sake of simplicity, we suggest using crow_all.h (by placing it in the same place as your main.cpp) and running the command g++ main.cpp -lpthread -O2 -o first (use clang instead of g++ if you prefer clang, or Visual Studio if you're on windows).

After building and running your .cpp file, you should be able to access your endpoint at http://localhost:18080. Opening this URL in your browser will show a white screen with "Hello world" typed on it.