Datadog provides automatic instrumentation for many popular languages, including Java, Python, and PHP, which requires no code changes. For C++, Datadog provides an OpenTracing-compatible tracer library. This library requires developers to manually add tracing code to their applications to generate spans and traces, meaning it is not automatically instrumented.

A. Java has a powerful auto-instrumentation agent that can be attached to a JVM application without any code modification to trace popular frameworks and libraries.

B. Python's dd-trace-py library can be used with ddtrace-run to automatically patch supported libraries and frameworks to enable tracing without manual code changes.

C. PHP's tracing extension, once enabled in the php.ini file, automatically instruments web requests and supported frameworks, providing tracing with minimal setup.

1. Datadog Documentation, "C++: Tracing Without Limits". Section: "Getting Started". States that developers need to "Add tracing to your code". Retrieved from https://docs.datadoghq.com/tracing/tracecollection/ddlibraries/cpp/.

2. Datadog Documentation, "Tracer Installation & Configuration". This page lists Java, Python, and PHP as having "Automatic instrumentation" capabilities. Retrieved from https://docs.datadoghq.com/tracing/tracecollection/libraryconfig/.

3. Datadog Documentation, "Java: Tracing Without Limits". Section: "Getting Started". Describes attaching the dd-java-agent.jar for automatic instrumentation. Retrieved from https://docs.datadoghq.com/tracing/tracecollection/ddlibraries/java/.