mediapipe/docs/getting_started/hello_world_desktop.md

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---
layout: default
title: Hello World! on Desktop (C++)
parent: Getting Started
nav_order: 5
---
# Hello World! on Desktop (C++)
{: .no_toc }
1. TOC
{:toc}
---
1. Ensure you have a working version of MediaPipe. See
[installation instructions](./install.md).
2. To run the [`hello world`] example:
```bash
$ 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!
```
3. The [`hello world`] example uses a simple MediaPipe graph in the
`PrintHelloWorld()` function, defined in a [`CalculatorGraphConfig`] proto.
```C++
::mediapipe::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](https://viz.mediapipe.dev) by pasting the
CalculatorGraphConfig content below into the visualizer. See
[here](../tools/visualizer.md) for help on the visualizer.
```bash
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 [`PassThroughCalculator`]s connected serially.
![hello_world graph](../images/hello_world.png)
4. 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`].
```c++
CalculatorGraph graph;
MP_RETURN_IF_ERROR(graph.Initialize(config));
MP_ASSIGN_OR_RETURN(OutputStreamPoller poller,
graph.AddOutputStreamPoller("out"));
MP_RETURN_IF_ERROR(graph.StartRun({}));
```
5. 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.
```c++
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"));
```
6. 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.
```c++
mediapipe::Packet packet;
while (poller.Next(&packet)) {
LOG(INFO) << packet.Get<string>();
}
```
[`hello world`]: https://github.com/google/mediapipe/tree/master/mediapipe/examples/desktop/hello_world/hello_world.cc
[`CalculatorGraphConfig`]: https://github.com/google/mediapipe/tree/master/mediapipe/framework/calculator.proto
[`PassThroughCalculator`]: https://github.com/google/mediapipe/tree/master/mediapipe/calculators/core/pass_through_calculator.cc
[`MakePacket`]: https://github.com/google/mediapipe/tree/master/mediapipe/framework/packet.h
[`StartRun`]: https://github.com/google/mediapipe/tree/master/mediapipe/framework/calculator_graph.h