c++ - 偶尔会出现段错误

Question

我正在尝试为一个 uni 项目制作一个随机数生成器。

我正在尝试实现一个函数来获取生成的此数字列表的周期(数字开始重复之前的时间)。

当我编译并运行它时，它返回 507(这是正确的句点)。

然而，大约 50% 的时间它会返回段错误。 知道发生了什么:

#include<iostream>
#include<fstream>
#include<vector>
#include<math.h>
#include<ctime>

using namespace std;

class Random
{
public:
// Constructor
Random(int a, int b, int m)
{
    this->setMagicNumbers(a,b,m);
}

// Function to set the magic numbers of the random number generator
void setMagicNumbers(int a, int b, int m)
{
    this->A = a;
    this->B = b;
    this->M = m;
}

// Function that returns a list of uniformly distributed random numbers
vector<double> GetUniform(int N, double initialValue = time(0))
{
    double currentNumber = initialValue;
    vector<double> RandomNumbers;
    for(int i = 0; i <= N; i++)
    {
        currentNumber = fmod((this->A*currentNumber) + this->B, this->M);
        RandomNumbers.push_back(currentNumber / this->M); // The number is normalised here
    }
    return RandomNumbers;
}

private:
int A, B, M;
};

class NumberList
{
public:
// Function to add an element to the list
void push(double x)
{
    this->v.push_back(x);
}

// Function to pop an element off the list
double pop()
{
    if(v.size() > 0)
    {
        int popped = v.back();
        v.pop_back();
        return popped;
    }
    else
    {
        cout << "Cannot pop element off empty list." << endl;
        return 0;
    }
    return 0;
}

// Function to get the value at a given location on the list
double getAt(int i)
{
    return this->v[i];
}

    // Function to set the value at a given location on the list
void setAt(int i, double value)
{
    this->v[i] = value;
}

// Function to find the size of the list
unsigned int size()
{
    return this->v.size();
}

// Function to get the vector itself
vector<double> getvector()
{
    return this->v;
}

// Function to set the value of the vector itself
void setVector(vector<double> vec)
{
    this->v = vec;
}

// Function to print the list of numbers as coordinates to a data file
void printCoordinates()
{
        ofstream data("coordinates.dat");
        for(unsigned int i = 0; i <= this->v.size(); i++)
        {
                data << this->v[i] <<  " " << this->v[i + 1] <<  "\n";
        }
        data.close();
}

// Function to print the list of numbers to the terminal
void print()
{
        for(unsigned int i = 0; i <= this->v.size(); i++)
        {
                cout << this->v[i] << endl;
        }
}

// Function to get the period of the list of numbers
int getPeriod()
{
    int i = 2;
    while(true)
    {
        if(isPeriod(i) == true)
        {
            return i;
        }
        else
        {
            i = i + 1;
        }
    }
}

private:
// Vector to hold the values for the list
vector<double> v;

// Function to test if 'i' is the period of the list
bool isPeriod(int i)
{
    for(int j = 0; j != (i-1); j++)
    {
        if(this->getAt(j) != this->getAt(i + j))
        {
            return false;
        }
    }
    return true;
}
};

int main()
{
Random RandNumGenerator(100,104001,714025);                // Create a new random number generator with given magic numbers
NumberList numbers;                                        // Create a blank list of numbers
numbers.setVector(RandNumGenerator.GetUniform(10000));     // Add 10000 random numbers to the list
numbers.printCoordinates();                                // Print out the random numbers as coordinates to a data file
cout << numbers.getPeriod() << endl;                       // Print out the period of the random number list
return 0;
}

提前致谢。

Answer 1

这一行可能会导致问题

for(unsigned int i = 0; i <= this->v.size(); i++)

有了它，您将大小用作最后一个索引，这是溢出，尝试为此更改它:

编辑:实际更改

for(unsigned int i = 0; i < this->v.size()-1; i++)

在循环中，您正在访问 vector 的第 i+1 个元素。

编辑:

这可能不会导致崩溃，但不是创建 N 个元素，而是创建 N+1

for(int i = 0; i <= N; i++)

如果为此更改:

for(int i = 0; i < N; i++)

编辑: 有修复

#include<iostream>
#include<fstream>
#include<vector>
#include<math.h>
#include<ctime>

using namespace std;

class Random
{
public:
// Constructor
Random(long a, long b, long m)
{
    this->setMagicNumbers(a,b,m);
}

// Function to set the magic numbers of the random number generator
void setMagicNumbers(long a, long b, long m)
{
    this->A = a;
    this->B = b;
    this->M = m;
}

// Function that returns a list of uniformly distributed random numbers
vector<double> GetUniform(int N, double initialValue = time(0))
{
    double currentNumber = initialValue;
    vector<double> RandomNumbers;
    for(int i = 0; i < N; i++)
    {
        currentNumber = fmod((this->A*currentNumber) + this->B, this->M);
        RandomNumbers.push_back(currentNumber / this->M); // The number is normalised here
    }
    return RandomNumbers;
}

private:
long A, B, M;
};

class NumberList
{
public:
// Function to add an element to the list
void push(double x)
{
    this->v.push_back(x);
}

// Function to pop an element off the list
double pop()
{
    if(v.size() > 0)
    {
        int popped = v.back();
        v.pop_back();
        return popped;
    }
    else
    {
        cout << "Cannot pop element off empty list." << endl;
        return 0;
    }
    return 0;
}

// Function to get the value at a given location on the list
double getAt(int i)
{
    return this->v[i];
}

    // Function to set the value at a given location on the list
void setAt(int i, double value)
{
    this->v[i] = value;
}

// Function to find the size of the list
unsigned int size()
{
    return this->v.size();
}

// Function to get the vector itself
vector<double> getvector()
{
    return this->v;
}

// Function to set the value of the vector itself
void setVector(vector<double> vec)
{
    this->v = vec;
}

// Function to print the list of numbers as coordinates to a data file
void printCoordinates()
{
        ofstream data("coordinates.dat");
        for(unsigned int i = 0; i < this->v.size()-1; i++)
        {
                data << this->v[i] <<  " " << this->v[i + 1] <<  "\n";
        }
        data.close();
}

// Function to print the list of numbers to the terminal
void print()
{
        for(unsigned int i = 0; i < this->v.size(); i++)
        {
                cout << this->v[i] << endl;
        }
}

// Function to get the period of the list of numbers
int getPeriod()
{
    int i = 2;
    while(true)
    {
        if(isPeriod(i) == true)
        {
            return i;
        }
        else
        {
            i = i + 1;
        }
    }
}

private:
// Vector to hold the values for the list
vector<double> v;

// Function to test if 'i' is the period of the list
bool isPeriod(int i)
{
    std::cout << "trying period " << i << endl;
    if (i >= v.size()) return true;
    for(int j = 0; j < v.size()-1; j++)
    {
        if(this->getAt(j) == this->getAt(i + j))
        {
            std::cout << "value at j " << this->getAt(j) << "value at i+j " << this->getAt(i+j) <<endl;
            return true;
        }
    }
    return false;
}
};

int main()
{
Random RandNumGenerator(100,104001,714025);                // Create a new random number generator with given magic numbers
NumberList numbers;                                        // Create a blank list of numbers
numbers.setVector(RandNumGenerator.GetUniform(10000));     // Add 10000 random numbers to the list
numbers.printCoordinates();                                // Print out the random numbers as coordinates to a data file
cout << numbers.getPeriod() << endl;                       // Print out the period of the random number list
return 0;
}