函數中的C++數組賦值問題

Question

這裏是C++新手，我遇到了一個我找不到的問題。

當我運行代碼下面我得到正確的結果我預期：

#include <iostream> 
#include <math.h> 

void factorize(int *factors, int number) 
{ 

    // declare vars 
    int index = 0; 

    // find factors of number 
    for (int x = 1; x <= number; ++x) { 
     // if x is a factor of number, save it to array 
     if (number % x == 0) { 
      std::cout << " Index: " << index << ", F: " << x << "\n"; 
      index++; 
     } 
    } 

} 

int main() 
{ 

    //declare vars 
    int triangle = 0; 
    int factors[] = {}; 

    //loop through all numbers 
    for (int x = 1; x <= 5; ++x) { 

     // calculate triangle value 
     std::cout << "initial triangle value: " << triangle << ", "; 
     triangle = triangle + x; 
     std::cout << "x value: " << x << " , new triangle value: " << triangle << "\n\n"; 

     // find factors of triangle number 
     factorize(factors, triangle); 
     std::cout<<"\n"; 

    } 

    return 0; 

} 

正確的結果：

initial triangle value: 0, x value: 1 , new triangle value: 1 

    Index: 0, F: 1 

initial triangle value: 1, x value: 2 , new triangle value: 3 

    Index: 0, F: 1 
    Index: 1, F: 3 

initial triangle value: 3, x value: 3 , new triangle value: 6 

    Index: 0, F: 1 
    Index: 1, F: 2 
    Index: 2, F: 3 
    Index: 3, F: 6 

initial triangle value: 6, x value: 4 , new triangle value: 10 

    Index: 0, F: 1 
    Index: 1, F: 2 
    Index: 2, F: 5 
    Index: 3, F: 10 

initial triangle value: 10, x value: 5 , new triangle value: 15 

    Index: 0, F: 1 
    Index: 1, F: 3 
    Index: 2, F: 5 
    Index: 3, F: 15 

但是，當我添加行因素[索引] = X;到因式分解函數，我得到了奇怪的結果。由於某些原因，三角形的值在主被修改。

#include <iostream> 
#include <math.h> 

void factorize(int *factors, int number) 
{ 

    // declare vars 
    int index = 0; 

    // find factors of number 
    for (int x = 1; x <= number; ++x) { 
     // if x is a factor of number, save it to array 
     if (number % x == 0) { 
      std::cout << " Index: " << index << ", F: " << x << "\n"; 
      factors[index] = x; 
      index++; 
     } 
    } 

} 

int main() 
{ 

    //declare vars 
    int triangle = 0; 
    int factors[] = {}; 

    //loop through all numbers 
    for (int x = 1; x <= 5; ++x) { 

     // calculate triangle value 
     std::cout << "initial triangle value: " << triangle << ", "; 
     triangle = triangle + x; 
     std::cout << "x value: " << x << " , new triangle value: " << triangle << "\n\n"; 

     // find factors of triangle number 
     factorize(factors, triangle); 
     std::cout<<"\n"; 

    } 

    return 0; 

} 

意想不到的結果（注意三角形值如何不言而喻：，，，但然後由於某些原因跳回）：

initial triangle value: 0, x value: 1 , new triangle value: 1 

    Index: 0, F: 1 

initial triangle value: 1, x value: 2 , new triangle value: 3 

    Index: 0, F: 1 
    Index: 1, F: 3 

initial triangle value: 3, x value: 3 , new triangle value: 6 

    Index: 0, F: 1 
    Index: 1, F: 2 
    Index: 2, F: 3 
    Index: 3, F: 6 

initial triangle value: 2, x value: 4 , new triangle value: 6 

    Index: 0, F: 1 
    Index: 1, F: 2 
    Index: 2, F: 3 
    Index: 3, F: 6 

initial triangle value: 2, x value: 5 , new triangle value: 7 

    Index: 0, F: 1 
    Index: 1, F: 7 

我錯過了什麼？

Answer 1

定義

int factors[] = {}; 

限定factors是一個空陣列int。它的每個索引都將超出範圍並導致未定義的行爲。第一個程序的作用是因爲你實際上沒有使用factors。

如果你想在C++中使用動態「數組」，你應該使用std::vector。

如果您事先知道尺寸，請使用該尺寸，或使用std::array。