如何在C ++中保存动态数组的值？

Question

编辑：问题已经解决，我正在访问由于while（）条件不正确而未初始化的数据。我已将其从OR更改为AND。它现在按预期工作。谢谢！

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我试图在C ++中找到两个数组之间的交集。我编写的代码可以执行我想要的操作，但是当我删除[]数组时，它会中断导致浮点异常。 （除以零？）如何在不导致程序内存泄漏的情况下保存我想要的值？

如果我省略delete []语句，这段代码完全符合我打算如何工作，但我相信这会导致内存泄漏。如果我省略语句largestIntersection = *（factorsa + i），它将返回1;我该怎么做才能在factora + i中保存值，然后删除数组以避免内存泄漏？

const int Fraction::findgcf(int a, int b) const{
    a = std::abs(a); //absoute value
    b = std::abs(b);

    int* factorsa = new int[a]; //dynamic array of ints to store factors of a
    int* factorsb = new int[b]; //dynamic array of ints to store factors of b


    int numFactorsa = 0;
    for(int i = 1; i <= a; i++){//iterate over the ints from 1 to a
        if(a % i == 0) {//if we find a factor of a
            *(factorsa + numFactorsa) = i;// and append that to the array
            numFactorsa++;
        }

    }

    int numFactorsb = 0;
    for(int i = 1; i <= b; i++){
        if(b % i == 0){
            *(factorsb + numFactorsb) = i;
            numFactorsb++;
        }
    }

    int biggestIntersection = 1;

     int i = 0, j = 0;
    while(i < numFactorsa || j < numFactorsb){//while we are in the bounds of the two arrays
        if(*(factorsa + i) < *(factorsb + j)){ //if the factor of a is less than the factor of b
            i++;                               //move the index of a up one
        } else if (*(factorsa + i) > *(factorsb + j)){ //if the factor of b is less than the factor of a
            j++;                                       //move the index of b up one
        } else {                                    //otherwise they must be equal
            biggestIntersection = *(factorsa + i); //so that is the new biggest intersection between the sets
            i++; j++;
        }
    }

    delete [] factorsa;
    delete [] factorsb;
    return biggestIntersection;

Answer 1

最大的问题 - 可能是导致错误的原因，尽管最小的例子会让它更清楚 - 是你正在访问你尚未初始化的内存。这可能会产生不可预测的行为。

int* factorsa = new int[a];没有将该数组中的每个int设置为零 - 数组的内容可能实际上是任何东西。稍后，在第一个for循环中，您可以设置某些数组位置的值，但不是全部。所以在你最后的for循环中，你无法知道你将要输出什么。它将取决于您询问new提供的内存位置的或多或少的随机内容。

（另外，作为评论说明，你的while循环条件是错误的。）

Answer 2

你真的应该使用std :: vector。那你就不用担心清理了。

const int Fraction::findgcf(int a, int b) const{
    a = std::abs(a); //absoute value
    b = std::abs(b);

    std::vector<int> factorsa(a);
    std::vector<int> factorsb(b);

    int numFactorsa = 0;
    for(int i = 1; i <= a; i++){//iterate over the ints from 1 to a
        if(a % i == 0) {//if we find a factor of a
            factorsa[numFactorsa] = i;// and append that to the array
            numFactorsa++;
        }

    }

    int numFactorsb = 0;
    for(int i = 1; i <= b; i++){
        if(b % i == 0){
            factorsb[numFactorsb] = i;
            numFactorsb++;
        }
    }

    int biggestIntersection = 1;

    int i = 0, j = 0;
    while(i < numFactorsa || j < numFactorsb){//while we are in the bounds of the two arrays
        if(factorsa[i] < factorsb[j]){ //if the factor of a is less than the factor of b
            i++;                               //move the index of a up one
        }
        else if (factorsa[i] > factorsb[j])
        {                                              //if the factor of b is less than the factor of a
            j++;                                       //move the index of b up one
        } else {                                    //otherwise they must be equal
            biggestIntersection = factorsa[i];      //so that is the new biggest intersection between the sets
            i++; j++;
        }
    }

    return biggestIntersection;
}