The vJoule API for C++ is installed along with the vJoule service. No other installations are required.

Here is a simple example using the installed API.

#include <iostream>
#include <cstdint>
#include <vjoule/vjoule_api.hh>

double computePi (uint64_t prec) {
    double res = 0;
    for (uint64_t i = 0 ; i < prec ; i++) {
        res += (4.0 / prec) / (1.0 + ((i - 0.5) * (1.0 / prec)) * ((i - 0.5) * (1.0 / prec)));
    }
    
    return res;
}

int main () {
    vjoule::vjoule_api api;
    
    auto m_begin = api.get_machine_current_consumption ();
    auto pi = computePi (100000000);
    auto m_end = api.get_machine_current_consumption ();
        
    auto m_diff = m_end - m_begin;

    std::cout << "RESULT : " << pi << " " << std::endl;
    std::cout << "CONSUMPTION : " << m_diff << std::endl;
    
    return 0;
}

The compilation needs to the link the library libvjoule_cpp.

$ g++ main.cc -lvjoule_cpp
$ ./a.out
RESULT : 3.14159 
CONSUMPTION : diff (time: 0.51s, pdu: 19.30J, cpu: 9.86J, ram: 0.31J, gpu: 0.00J)

The API is base on the type vjoule::vjoule_api. This type is used to retreive the consumption of the machine from different components (enabled by the configuration of the vjoule_service).

The C++ API uses the vjoule service to retrieve the consumption of the components. The service must be running, using the simple core plugin. The getCurrentMachineConsumption function triggers a consumption reading by the service, and retrieves the values of each enabled component (disabled components are set to 0). So there is no need to wait for the next iteration of the service to read a value. In fact, the service can be configured with a frequency of 0 (i.e., no iteration at all).