Read CPU on Linux C++

Question

I'm developing a server auditor in c++. The big problem i have here is that when I try to read the CPU usage, the first core gets calculated correctly, but the rest looks like this:

Core 0 percentage: 3.48259%

Core 1 percentage: 8200%

Core 2 percentage: 2562.12%

Core 3 percentage: -905.97%

The code i'm using is below

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>


#include <boost/foreach.hpp>
#ifdef WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif // win32

#include <vector>
using namespace std;


void sleepcp(int milliseconds);

void sleepcp(int milliseconds) // cross-platform sleep function
{
    #ifdef WIN32
    Sleep(milliseconds);
    #else
    usleep(milliseconds * 1000);
    #endif // win32
}
string convertIntToString(int i){
    string result;
    ostringstream convert;
    convert << i;
    result = convert.str();
    return result;
}
int convertStringToInt(string s){
    return atoi(s.c_str());
}
bool is_digits(const std::string &str) {
    return std::all_of(str.begin(), str.end(), ::isdigit); // C++11
}
int getNumberOfCores(){
    ifstream cpuinfo;
    cpuinfo.open("/proc/cpuinfo",ios::in);
    string word;
    int cpucount = 0;
    if (cpuinfo.is_open()) {
        while ( cpuinfo >> word ) {
            if(word == "processor"){
                cpucount++;
            }
            }
        cpuinfo.close();
    }

    else cout << "Unable to open file"; 
    return cpucount;
}
string splitLineAt(const std::string str, int position){
    std::istringstream buf(str);
    std::istream_iterator<std::string> beg(buf), end;

    std::vector<std::string> tokens(beg, end);
    return tokens[position];
}

int getTotalTicks(string line){
    int total_ticks = convertStringToInt(splitLineAt(line,1)) +     convertStringToInt(splitLineAt(line,2)) + convertStringToInt(splitLineAt(line,3)) + convertStringToInt(splitLineAt(line,4)) + convertStringToInt(splitLineAt(line,5)) + convertStringToInt(splitLineAt(line,6)) + convertStringToInt(splitLineAt(line,7));
    return total_ticks;
}
int getWorkTicks(string line){
    int work_ticks = convertStringToInt(splitLineAt(line,1)) + convertStringToInt(splitLineAt(line,2)) + convertStringToInt(splitLineAt(line,3));
    return work_ticks;
}
int *prev_total_ticks;
int *prev_work_ticks;
double getCorePercentage(int i){

    ifstream currentUsage;
    currentUsage.open("/proc/stat",ios::in);
    string line;    
    if(currentUsage.is_open()){

        while(getline(currentUsage,line)){
            if(line.at(0) == 'c' && line.at(1) == 'p' && line.at(2) == 'u'){
                if(line.at(3) == convertIntToString(i).at(0)){
                    int total_ticks = getTotalTicks(line);
                    int work_ticks = getWorkTicks(line);                    
                    int total_over_period =  total_ticks - (prev_total_ticks[i-1]);
                    int work_over_period =   work_ticks - (prev_work_ticks[-1]);
                    cout << prev_total_ticks[i-1] << "\n";
                    cout << prev_work_ticks[i-1] << "\n";
                    prev_work_ticks[i-1] = work_ticks;
                    prev_total_ticks[i-1] = total_ticks;

                    return ((double)work_over_period / (double)total_over_period) * 100.0;
                }
            }
        }
    }
}


int main(){
    prev_total_ticks = new int[getNumberOfCores()];
    prev_work_ticks = new int[getNumberOfCores()];
    for(int i = 0; i < getNumberOfCores(); i++){
        prev_total_ticks[i] = 0;
        prev_work_ticks[i] = 0;
    }
    while (true){
        for(int i = 0; i < getNumberOfCores(); i++){
            cout << "Core "<<i<<" percentage: "<< getCorePercentage(i) << "%\n";
        }
        sleepcp(2000);
    }
    return 0;
}

The calculation in getCorePercentage is the culprit i belive, but i'm not sure.... Before when i was just checking one core at a time it worked perfectly...

Any ideas on how to fix this?

Answer 1

int work_over_period =   work_ticks - (prev_work_ticks[-1]);
                                                       ^^

I'm sure you want to say i-1 there.