Question

我遇到了一个我不太了解的问题。我正在Lubuntu的QTcreator中运行此代码，在代码之后说明了我遇到的问题。这是一个简单的程序，使用分叉运行一些进程，这些分叉使用蒙特卡洛方法近似于Pi。

SIM.h

  #include <complex>
#include <iostream>
#include <valarray>

const double PI = 3.141592653589793238460;

typedef std::complex<double> Complex;
typedef std::valarray<Complex> CArray;

// Cooley–Tukey FFT (in-place, divide-and-conquer)
// Higher memory requirements and redundancy although more intuitive
void fft(CArray& x)
{
    const size_t N = x.size();
    if (N <= 1) return;

    // divide
    CArray even = x[std::slice(0, N/2, 2)];
    CArray  odd = x[std::slice(1, N/2, 2)];

    // conquer
    fft(even);
    fft(odd);

    // combine
    for (size_t k = 0; k < N/2; ++k)
    {
        Complex t = std::polar(1.0, -2 * PI * k / N) * odd[k];
        x[k    ] = even[k] + t;
        x[k+N/2] = even[k] - t;
    }
}

// Cooley-Tukey FFT (in-place, breadth-first, decimation-in-frequency)
// Better optimized but less intuitive
// !!! Warning : in some cases this code make result different from not optimased version above (need to fix bug)
// The bug is now fixed @2017/05/30 
void fft(CArray &x)
{
    // DFT
    unsigned int N = x.size(), k = N, n;
    double thetaT = 3.14159265358979323846264338328L / N;
    Complex phiT = Complex(cos(thetaT), -sin(thetaT)), T;
    while (k > 1)
    {
        n = k;
        k >>= 1;
        phiT = phiT * phiT;
        T = 1.0L;
        for (unsigned int l = 0; l < k; l++)
        {
            for (unsigned int a = l; a < N; a += n)
            {
                unsigned int b = a + k;
                Complex t = x[a] - x[b];
                x[a] += x[b];
                x[b] = t * T;
            }
            T *= phiT;
        }
    }
    // Decimate
    unsigned int m = (unsigned int)log2(N);
    for (unsigned int a = 0; a < N; a++)
    {
        unsigned int b = a;
        // Reverse bits
        b = (((b & 0xaaaaaaaa) >> 1) | ((b & 0x55555555) << 1));
        b = (((b & 0xcccccccc) >> 2) | ((b & 0x33333333) << 2));
        b = (((b & 0xf0f0f0f0) >> 4) | ((b & 0x0f0f0f0f) << 4));
        b = (((b & 0xff00ff00) >> 8) | ((b & 0x00ff00ff) << 8));
        b = ((b >> 16) | (b << 16)) >> (32 - m);
        if (b > a)
        {
            Complex t = x[a];
            x[a] = x[b];
            x[b] = t;
        }
    }
    //// Normalize (This section make it not working correctly)
    //Complex f = 1.0 / sqrt(N);
    //for (unsigned int i = 0; i < N; i++)
    //  x[i] *= f;
}


int main()
{
    const Complex test[] = { 1.0, 1.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0 };
    CArray data(test, 8);

    // forward fft
    fft(data);

    std::cout << "fft" << std::endl;
    for (int i = 0; i < 8; ++i)
    {
        std::cout << data[i] << std::endl;
    }

    }
    return 0;
}

SIM.cpp

#ifndef SIM_H
#define SIM_H

#include <random>
#include "SIM.h"
#include <math.h>
#include <ctime>
#include <iostream>
#include <chrono>
#include <fstream>
#include <string>
using namespace std;

class Sim{
   private:
       double xCoor, yCoor, resultPyth, inCircle, outsideCircle, approxPi, totalRead;
       int runs, totalInsideCircle;
       string FILENAME, FILENAME_END;
       std::vector<double> piVector;
   public:
       Sim(){}
       explicit Sim(int pRuns);
       ~Sim() = default;

       bool isInCircle();
       void calcPiAndPrint();
};

#endif

main.cpp

#include "SIM.h"
#include <chrono>
#include <ctime>
#include <fstream>
#include <iostream>
#include <math.h>
#include <stdio.h>

Sim::Sim(int pRuns) {
  runs = pRuns;
}

bool Sim::isInCircle() {
  std::random_device rd;
  std::mt19937 mt(rd());

  std::random_device rd1;
  std::mt19937 mt1(rd1());

  std::uniform_real_distribution<double> dist{-1.0, 1.0};
  std::uniform_real_distribution<double> dist1{-1.0, 1.0};
  for (int i = 0; i < runs; i++) {
    double x = dist(mt);
    double y = dist1(mt1);

    xCoor = x;
    yCoor = y;
    resultPyth = sqrt(pow(x, 2) + pow(y, 2));
    if (resultPyth <= 1.0) {
      totalInsideCircle++;
    }
  }
  return true;
}


void Sim::calcPiAndPrint() {
  cout << "Inside circle: " << totalInsideCircle << endl; <-- a 10-digit number
  cout << "Runs : " << runs << endl; //<-- a 10-digit number, should be 1000
  cout << "Approximation of Pi = " << (totalInsideCircle / runs) * 4 << endl;
}

很抱歉，我尽可能地缩短了代码量。所以要解决这个问题。创建对象时传递给构造函数的整数将保存在变量#include <iostream> #include <string> #include "Sim.h" #include <stdio.h> #include <sys/types.h> #include <sys/wait.h> #include <stdlib.h> #include <unistd.h> using namespace std; using std::cerr; using std::endl; int main () { Sim *sim; pid_t childPid; pid_t pids[10]; for(int i = 0; i < 5; i++ ) { if((pids[i] = fork()) < 0){ perror("failed to fork..."); return 1; } else if(pids[i] == 0){ sim= new Sim(1000); sim->isInCircle(); exit(0); } else{ } } int n = 10; int status; pid_t pid; while(n > 0){ pid = wait(&status); sim->calcPiAndPrint(); printf("Child with pid %ld exited with status 0x%x.\n", (long)pid, status); n--; } delete sim; return 0; }中。在我的代码中，我将其设置为1000，但是当我调用int runs时，它将打印一个10位数字。同样访问calcPiAndPrint()将导致EXC_BAD_ACCESS错误，但也会打印10位数字。我通常在初始化变量时没有任何问题，但是我无法弄清楚这里出了什么问题。我确实怀疑我的叉子与问题有关。任何帮助表示赞赏。

Answer 1

如果我理解正确，那么您在这里的操作如下：

您将当前流程分为5个新进程。
这些子进程中的每个子进程都会创建一个新的Sim对象，调用isInCircle()方法，然后退出。
父进程调用sim->calcPiAndPrint()。

请注意，父进程从未创建Sim对象。父进程中的指针sim尚未初始化，因此尝试取消引用（例如，通过调用方法或尝试访问其未指向的对象的成员）将导致不确定的行为。在这种情况下，通常意味着它将尝试访问无效或垃圾内存，并且理想情况下会崩溃，以便您可以注意到您的错误……

标头中的C ++整数初始化

1 个答案: