C++ Examples¶

Applying DDTrace in C + + code requires modifying business code and manually embedding points in existing business code. This document demonstrates how to bury points in C + + code with a simple read file demo.

Install Libraries and Dependencies¶

Linux/macOSWindows

Download DDTrace-C++ SDK

git clone https://github.com/DataDog/dd-opentracing-cpp

Compile and install the SDK

# Install dependencies
cd dd-opentracing-cpp && sudo scripts/install_dependencies.sh

# Compile and install
mkdir .build && cd .build && cmake .. && make && make install

If you have problems compiling the SDK, you can temporarily test it with the prepared header file 5 and dynamic library 6 of Guance Cloud.

Coming Soon...

cmake installation

Cmake may not be installed to a higher version through yum or apt-get. It is recommended to download the latest version directly from its official website. You can also use the observation cloud hosted source or Windows binary directly.

# Install cmake from source
wget https://static.guance.com/gfw/cmake-3.24.2.tar.gz
tar -zxvf cmake-3.24.2.tar.gz
./bootstrap --prefix=/usr/local
make
make install

# Verify the current version
cmake --version
cmake version 3.24.2

Gcc install version 7. x:

yum install centos-release-scl
yum install devtoolset-7-gcc*
scl enable devtoolset-7 bash
which gcc
gcc --version

C++ Code Sample¶

The following C + + code demonstrates the basic trace burial operation, which simulates a business that reads a local disk file.

#include <datadog/opentracing.h>
#include <datadog/tags.h>

#include <stdarg.h>
#include <memory> 
#include <chrono>
#include <fstream>
#include <string>
#include <chrono>
#include <thread>
#include <sys/stat.h>

datadog::opentracing::TracerOptions tracer_options{"", 0, "compiled-in-example"};
auto tracer = datadog::opentracing::makeTracer(tracer_options);

std::ifstream::pos_type filesize(const char* filename) {
    std::ifstream in(filename, std::ifstream::ate | std::ifstream::binary);
    return in.tellg(); 
}

std::string string_format(const std::string fmt_str, ...) {
    int final_n, n = ((int)fmt_str.size()) * 2;
    std::unique_ptr<char[]> formatted;
    va_list ap;
    while(1) {
        formatted.reset(new char[n]);
        strcpy(&formatted[0], fmt_str.c_str());
        va_start(ap, fmt_str);
        final_n = vsnprintf(&formatted[0], n, fmt_str.c_str(), ap);
        va_end(ap);
        if (final_n < 0 || final_n >= n)
            n += abs(final_n - n + 1);
        else
            break;
    }
    return std::string(formatted.get());
}

int runApp(const char* f) {
    auto span_a = tracer->StartSpan(f);
    span_a->SetTag(datadog::tags::environment, "production");
    span_a->SetTag("tag", "app-ok");
    span_a->SetTag("file_len", string_format("%d", filesize(f)));
}

int main(int argc, char* argv[]) {
    for (;;) {
        runApp(argv[0]);
        runApp("file-not-exists");
        std::this_thread::sleep_for(std::chrono::milliseconds(1000));
    }

    tracer->Close();
    return 0;
}

Compile and Run¶

LD_LIBRARY_PATH=/usr/local/lib64 g++ -std=c++14 -o demo demo.cc -ldd_opentracing -I ./dd-opentracing-cpp/deps/include
LD_LIBRARY_PATH=/usr/local/lib64  DD_AGENT_HOST=localhost DD_TRACE_AGENT_PORT=9529 ./demo

Here you can put libdd_opentracing.so and the corresponding header file into any directory and adjust the LD_LIBRARY_PATH and -I parameters.

After running the program for a period of time, you can see trace data similar to the following in Guance Cloud:

Environment Variable Support¶

Supported Environment Variables¶

The following environment variables support specifying some configuration parameters of ddtrace when starting the program, and their basic form is:

DD_XXX=<env-value> DD_YYY=<env-value> ./demo

Several commonly used ENVs are as follows. For more ENV support, see DDTrace Original.

Key	Default Value	Description
`DD_VERSION`	-	Set the application version, such as 1.2.3、2022.02.13
`DD_AGENT_HOST`	`localhost`	Set DataKit address
`DD_TRACE_AGENT_PORT`	-	Set the receiving port for DataKit trace data. You need to manually specify HTTP port for DataKit (typically 9529)
`DD_ENV`	-	Set the current application environment, such as prod, pre-prod, etc.
`DD_SERVICE`	-	Set the application service name
`DD_TRACE_SAMPLING_RULES`	-	Here, a JSON array is used to represent the sampling setting (the sampling rate is applied in the order of the array), where `sample_rate` is the sampling rate and the value range is `[0.0, 1.0]`。 Example 1: Set the global sampling rate to 20%: `DD_TRACE_SAMPLE_RATE='[{"sample_rate": 0.2}]' ./my-app` Example 2: If the service name is generic `app1.`, and the span name is `abc`, the sampling rate is set to 10%, except that the sampling rate is set to 20%: `DD_TRACE_SAMPLE_RATE='[{"service": "app1.", "name": "b", "sample_rate": 0.1}, {"sample_rate": 0.2}]' ./my-app`
`DD_TAGS`	-	Here you can inject a set of global tags that will appear in each span and profile data. Multiple tags can be separated by spaces and English commas, such as `layer:api,team:intake`、`layer:api team:intake`