build-a-c++-app-with-cockroachdb.md

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Build a C++ App with CockroachDB and libpqxx	Learn how to use CockroachDB from a simple C++ application with a low-level client driver.	true	false	docs_hello_world_c++_libpgxx

This tutorial shows you how build a simple C++ application with CockroachDB and the C++ libpqxx driver.

We have tested the C++ libpqxx driver enough to claim beta-level support. If you encounter problems, please open an issue with details to help us make progress toward full support.

Step 1. Start CockroachDB

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Step 2. Create a database and a user

{% include {{page.version.version}}/app/create-a-database.md %}

Step 3. Install the libpq and libpqxx drivers

1. Install libpq on your machine. For example, on macOS:

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   brew install libpq

2. Install the libpqxx driver, using CMake or the configure script provided in the libpqxx repo.

   {{site.data.alerts.callout_info}} If you are running macOS, you need to install version 4.0.1 or higher of the libpqxx driver. {{site.data.alerts.end}}

Step 4. Get the C++ code

Download the basic-sample.cpp file, or create the file yourself and copy the code into it.

Step 5. Run the code

You'll first run code to create a table and insert some rows, and then you'll run code to read and update values as an atomic transaction.

Basic statements

Use the following code to connect as the user you created earlier and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.

You will need to open basic-sample.cpp, and edit the connection configuration parameters:

• Replace the value for username with the user you created earlier.
• Replace the value for password with the password you created for your user.
• Replace the value for host with the host to your cluster.
• Replace the value for port with the port to your cluster.

Use the following code to connect and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.

You will need to open basic-sample.cpp, and edit the following:

• Replace the connection string in the code with the connection string that was provided in the CockroachCloud Console earlier.
• Replace defaultdb in the connection string with bank to connect to the bank database you created earlier.

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{% include {{ page.version.version }}/app/basic-sample.cpp %}

To build the basic-sample.cpp source code to an executable file named basic-sample, run the following command from the directory that contains the code:

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$ g++ -std=c++17 basic-sample.cpp -lpq -lpqxx -o basic-sample

Then run the basic-sample file from that directory:

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$ ./basic-sample

Transaction (with retry logic)

Next, use the following code to again connect as the user you created earlier but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

You will need to open basic-sample.cpp, and edit the connection configuration parameters:

• Replace the value for username with the user you created earlier.
• Replace the value for password with the password you created for your user.
• Replace the value for host with the host to your cluster.
• Replace the value for port with the port to your cluster.

Next, use the following code to again connect, but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

You will need to open txn-sample.cpp, and edit the following:

• Replace the connection string in the code with the connection string that was provided in the CockroachCloud Console earlier.
• Replace defaultdb in the connection string with bank to connect to the bank database you created earlier.

{{site.data.alerts.callout_info}} CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code. {{site.data.alerts.end}}

Download the txn-sample.cpp file, or create the file yourself and copy the code into it.

{% include copy-clipboard.html %}

{% include {{ page.version.version }}/app/txn-sample.cpp %}

To build the txn-sample.cpp source code to an executable file named txn-sample, run the following command from the directory that contains the code:

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$ g++ -std=c++17 txn-sample.cpp -lpq -lpqxx -o txn-sample

Then run the txn-sample file from that directory:

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$ ./txn-sample

After running the code, use the built-in SQL client to verify that funds were transferred from one account to another:

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$ cockroach sql --url 'postgresql://{username}:{password}@{host}:{port}/{cluster_name}.bank?sslmode=verify-full&sslrootcert={path/to/ca.crt}' -e 'SELECT id, balance FROM accounts'

id | balance
+----+---------+
 1 |     900
 2 |     350
(2 rows)

What's next?

Read more about using the C++ libpqxx driver.

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