模板程序不断崩溃

Question

My program will compile and run fine but it crashes when im in the program. Any idea why?

template<class T>
T findFeq (T arr1[], T target, T arrSize);

template<class T>
    T findFreq (T arr1[], T target, T arrSize){
    int count = 0;
    for(int i = 0; i < arrSize; i++){
        if (target == arr1[i])
            count++;
    }
    return count;
}

#include "Ex1.h"
#include <iostream>
using namespace std;

void fillIntArray(int arr1[], int arrSize, int& spacesUsed);
void fillDoubleArray(double arr1[], int arrSize, int& spacesUsed);

int main(){
    const int SIZE = 1000;
    int itarget = 42;
    double dTarget = 42.0;
    int ispacesUsed;
        double dspacesUsed;
    int iArray[SIZE];
    double dArray[SIZE];

    fillIntArray(iArray,SIZE,ispacesUsed);
    cout << findFreq(iArray,itarget,ispacesUsed) << endl;

    fillDoubleArray(dArray,SIZE,dspacesUsed);
    cout << findFreq(dArray,dTarget,dspacesUsed) << endl;

    return 0;
}

void fillIntArray(int arr1[], int arrSize, int& spacesUsed){
    int maxSize;
    cout << "How many numbers shall i put into the Array? ";
    cin >> maxSize;
    for (int i = 0; i < maxSize; i++){
            arr1[i] = (rand()% 100);
        spacesUsed++;
    }
}

void fillDoubleArray(double arr1[], int arrSize, int& spacesUsed){
    int maxSize,i = 0;
    cout << "How many numbers shall i put into the Array? ";
    cin >> maxSize;
    while (i < maxSize){
        cout << "Enter number to put in Array: ";
        cin >> arr1[i];
        i++;
    }
}

Answer 1

There are several problems. But the problem which will cause a crash is,

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

Just imagine what if you enter maxSize greater than arrSize ? The buffer will overflow and it causes either an Undefined behavior or crash . Same is applicable for while loop meant for filling double array.

On the side note, change the signature for findFeq to:

template<class T>
T findFeq (T arr1[], T target, unsigned int arrSize); // arrSize must be of integer type

Answer 2

Problems:

• maxSize can be greater than SIZE --> array out of bounds

• T findFeq (T arr1[], T target, size_t arrSize); --> array size should not depend on type T

• fillDoubleArray(dArray,SIZE, dspacesUsed ); --> this is dangerous, the 3rd argument sdpacesUsed should be int& not double& . This should not pass compile.