hello_world_cpp title: Hello World! in C++ parent: MediaPipe in C++ grand_parent: Getting Started nav_order: 1¶

Hello World! in C++¶

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Attention: Thanks for your interest in MediaPipe! We have moved to https://developers.google.com/mediapipe as the primary developer documentation site for MediaPipe as of April 3, 2023.

Ensure you have a working version of MediaPipe. See installation instructions.

To run the hello world example:

$ git clone https://github.com/google/mediapipe.git
$ cd mediapipe

$ export GLOG_logtostderr=1
# Need bazel flag 'MEDIAPIPE_DISABLE_GPU=1' as desktop GPU is not supported currently.
$ bazel run --define MEDIAPIPE_DISABLE_GPU=1 \
    mediapipe/examples/desktop/hello_world:hello_world

# It should print 10 rows of Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!
# Hello World!

The hello world example uses a simple MediaPipe graph in the PrintHelloWorld() function, defined in a CalculatorGraphConfig proto.

absl::Status PrintHelloWorld() {
  // Configures a simple graph, which concatenates 2 PassThroughCalculators.
  CalculatorGraphConfig config = ParseTextProtoOrDie<CalculatorGraphConfig>(R"(
    input_stream: "in"
    output_stream: "out"
    node {
      calculator: "PassThroughCalculator"
      input_stream: "in"
      output_stream: "out1"
    }
    node {
      calculator: "PassThroughCalculator"
      input_stream: "out1"
      output_stream: "out"
    }
  )");

You can visualize this graph using MediaPipe Visualizer by pasting the CalculatorGraphConfig content below into the visualizer. See here for help on the visualizer.

    input_stream: "in"
    output_stream: "out"
    node {
      calculator: "PassThroughCalculator"
      input_stream: "in"
      output_stream: "out1"
    }
    node {
      calculator: "PassThroughCalculator"
      input_stream: "out1"
      output_stream: "out"
    }

This graph consists of 1 graph input stream (in) and 1 graph output stream (out), and 2 PassThroughCalculators connected serially.

hello_world graph

Before running the graph, an OutputStreamPoller object is connected to the output stream in order to later retrieve the graph output, and a graph run is started with StartRun.

CalculatorGraph graph;
MP_RETURN_IF_ERROR(graph.Initialize(config));
MP_ASSIGN_OR_RETURN(OutputStreamPoller poller,
                    graph.AddOutputStreamPoller("out"));
MP_RETURN_IF_ERROR(graph.StartRun({}));

The example then creates 10 packets (each packet contains a string “Hello World!” with Timestamp values ranging from 0, 1, … 9) using the MakePacket function, adds each packet into the graph through the in input stream, and finally closes the input stream to finish the graph run.
```
for (int i = 0; i < 10; ++i) {
  MP_RETURN_IF_ERROR(graph.AddPacketToInputStream("in",
                     MakePacket<std::string>("Hello World!").At(Timestamp(i))));
}
MP_RETURN_IF_ERROR(graph.CloseInputStream("in"));
```
Through the OutputStreamPoller object the example then retrieves all 10 packets from the output stream, gets the string content out of each packet and prints it to the output log.
```
mediapipe::Packet packet;
while (poller.Next(&packet)) {
  ABSL_LOG(INFO) << packet.Get<string>();
}
```