偶尔会出现分段错误

Question

我正在尝试为uni项目创建一个随机数生成器。

我正在尝试实现一个函数来获取生成此数字列表的时间段（数字开始重复之前多久）。

当我编译并运行它时，它返回507（这是正确的句号）。

然而，大约50％的时间它会返回分段错误。 不知道发生了什么：

#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

此行可能会导致问题

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

有了它，你使用size作为最后一个索引，这是溢出，尝试改变它：

编辑：实际改变

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

在循环中，您正在访问向量的第i + 1个元素。

编辑：

这可能不会导致崩溃，而是创建N个元素而不是创建N + 1

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

为此改变：

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

编辑： 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;
}

Answer 2

稍微玩了一下，我最初认为你的双打矢量以某种方式被破坏了。我发现，如果你把它的大小调整到你想要的确切值 - 这是一个已知的值 - seg错误停止：

vector<double> RandomNumbers(N); // In GetUniform()

通过gdb运行它是不确定的，因为它看起来好像堆栈已损坏。我还发现当我更改push_back()只是为了取0：

RandomNumbers.push_back(0.0);

而不是标准化的数字，即使没有向量的初始大小（上图），它也能正常工作，这表明其中一个变量存在问题。

我还发现如果我将currentNumber设置为1，比如说，而不是调用fmod() - 即使是最初的所有内容，我也没有出现seg错误：

currentNumber = 1;

这种情况表明它可能与使用fmod()

有关

有趣的是，然后我完全取消了对push_back的调用，发现仍然有段错误。对不起，我没有比这更多的帮助，但看起来好像在这个地区某处发生了某种腐败。

Answer 3

在C++数组索引中，vector将来自0..size - 1，并且您在代码内部（GetUniform内部，printCoordinates内部误用了它） ，...）除了printCoordinates中你最后写的this->v[i + 1]之外，它将被转换为this->v[this->v.size() + 1]，它是最后一个有效索引之后的2个索引。

但我认为您的错误来源位于getPeriod和isPeriod，请查看它从0开始到i - 1并检查该索引是否与索引{{1}处的项目匹配}，所以如果i + j变为i且大小为500，那么在更糟糕的情况下，您访问的size() - 1实际上比上一个有效索引大，您肯定会遇到分段错误。现在解决它检查您的索引并且永远不会超出v[499 + 498]大小的末尾，这意味着您永远不应该使用索引＆gt; vector