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

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.

Before you begin

{% include {{page.version.version}}/app/before-you-begin.md %}

Step 1. Install the libpqxx driver

Install the C++ libpqxx driver as described in the official documentation.

{{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 2. Create the maxroach user and bank database

{% include {{page.version.version}}/app/create-maxroach-user-and-bank-database.md %}

Step 3. Generate a certificate for the maxroach user

Create a certificate and key for the maxroach user by running the following command. The code samples will run as this user.

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$ cockroach cert create-client maxroach --certs-dir=certs --ca-key=my-safe-directory/ca.key

Step 4. Run the C++ code

Now that you have a database and a user, you'll 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

First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.

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

{% include copy-clipboard.html %}

{% 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:

{% include copy-clipboard.html %}

$ g++ -std=c++11 basic-sample.cpp -lpq -lpqxx -o basic-sample

Then run the basic-sample file from that directory:

{% include copy-clipboard.html %}

$ ./basic-sample

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user 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.

{{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:

{% include copy-clipboard.html %}

$ g++ -std=c++11 txn-sample.cpp -lpq -lpqxx -o txn-sample

Then run the txn-sample file from that directory:

{% include copy-clipboard.html %}

$ ./txn-sample

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

{% include copy-clipboard.html %}

$ cockroach sql --certs-dir=certs -e 'SELECT id, balance FROM accounts' --database=bank

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

Step 2. Create the maxroach user and bank database

{% include {{page.version.version}}/app/insecure/create-maxroach-user-and-bank-database.md %}

Step 3. Run the C++ code

Now that you have a database and a user, you'll 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

First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.

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

{% include copy-clipboard.html %}

{% include {{ page.version.version }}/app/insecure/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:

{% include copy-clipboard.html %}

$ g++ -std=c++11 basic-sample.cpp -lpq -lpqxx -o basic-sample

Then run the basic-sample file from that directory:

{% include copy-clipboard.html %}

$ ./basic-sample

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user 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.

{{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/insecure/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:

{% include copy-clipboard.html %}

$ g++ -std=c++11 txn-sample.cpp -lpq -lpqxx -o txn-sample

Then run the txn-sample file from that directory:

{% include copy-clipboard.html %}

$ ./txn-sample

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

{% include copy-clipboard.html %}

$ cockroach sql --insecure -e 'SELECT id, balance FROM accounts' --database=bank

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

What's next?

Read more about using the C++ libpqxx driver.

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