总线错误：C二进制和线性搜索程序中的10

Question

#include <stdio.h>
#include <stdlib.h>

void arrayCopy(int fromArray[], int toArray[], int size){
    int i = 0;

    while(i < size){
        toArray[i] = fromArray[i];
        i++;
    }
}


void sort(int arr[], int size){
    int i, j;
    int temp;

    //simple sorting method comparing values next to each other
    //bigger value is moved further down the array
    //loops through "size" times
    for(i = 0; i < size; i++){
       for(j = 0; j < size - 1; j++){
            if(arr[j] > arr[j+1])
            {
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
}

int linSearch(int arr[], int size, int target, int* numComparisons){
    int i;
    *numComparisons = 0;

    //if target is found loop will exit prematurely returning location in array
    //if target is not found loop will exit and return -1
    for(i = 0; i < size; i++){
        *numComparisons = *numComparisons + 1;  //tracks number of comparisons made
        if(arr[i] == target){
            return i;
        }
    }
    return -1;
} 

int binSearch(int arr[], int size, int target, int* numComparisons){
    int i;
    int first, last, mid;

    first = 0;
    last = size - 1;
    mid = (first + last) / 2;
    *numComparisons = 0;

    while(first <= last){
        if(arr[mid] == target){
            *numComparisons = *numComparisons + 1;
            return mid;
        } else if(arr[mid] < target){
            *numComparisons = *numComparisons + 1;
            first = mid + 1;
        } else{
            *numComparisons = *numComparisons + 1;
            last = mid - 1;
        }
    }

    return -1;


}

int main(){
    int i = 0;
    int j, k, l;
    int size = 0;
    int dynamicSize = 100;
    int val;
    int *arr1, *arr2;
    int *temp;
    int *numComparisons1, *numComparisons2;


    arr1 = (int*)malloc(dynamicSize * sizeof(int));

    printf("Please input your values.\n Terminate input with the value -999.\n");

    while(val != -999){
        //reads values and assigns them to array
        scanf("%d", &val);
        if(size >= dynamicSize){
            temp = (int*)malloc(dynamicSize * 2 * sizeof(int));
            for ( i = 0 ; i < dynamicSize ; i++){
                temp[i] = arr1[i];
            }
            free(arr1);
            arr1 = temp;
            dynamicSize = dynamicSize * 2;
        }
        arr1[i] = val;
        i = i + 1;
        size = size + 1;

    }
    val = 0;

     //Second array for binary search
     arr2 = (int*)malloc(dynamicSize * sizeof(int));
     arrayCopy(arr1, arr2, size);
     sort(arr2, size);

    printf("Please enter the number you would like to find.\n Terminate search with value -999.\n");
    while(val != -999){
        scanf("%d", &val);
        k = linSearch(arr1, size, val, numComparisons1);
        j = binSearch(arr2, size, val, numComparisons2);
        if(k == -1){
             printf("The value was not found.\n");
        }else{
             printf("Unsorted Array:\n The value is located at %d\n The number of comparisons made was %d\n", k, *numComparisons1);
             printf("Sorted Array:\n The value is located at %d\n The number of comparisons made was %d\n", j, *numComparisons2);
    }
  }

    return 0;
}

The program is supposed to take in user input and store it in an array. When the user enters the value -999 the program will then create a second array, which is a copy of the first. The second array will then be sorted through the sort function for use in the binary search function. The program then asks for the user to enter a value and that value will be checked for by the linear search and the binary search. If the value is found the functions will return the number of comparisons made and where the value is in the array. If it is not found the program will return that the value was not found. This repeats until the user terminates the program by inputing the value -999. The problem seems to be with the binary search. When included the program produces bus error : 10, but when I comment out the call to the binSearch function the program works fine.

Answer 1

You should check for available space before storing the value into the array:

int *arr1 = malloc(sizeof(int));
size_t dynamicSize = 1;
size_t size = 0;

// reads values and assigns them to array
while (scanf("%d", &val) == 1 && val != -999) {
    if (size >= dynamicSize) {
        arr1 = realloc(arr1, dynamicSize * 2 * sizeof(*arr1));
        dynamicSize = dynamicSize * 2;
    }
    arr1[size++] = val;
}

Your binary lookup function is incorrect:

• You must recompute mid for each iteration in the loop
• You do not compute the number of comparisons correctly
• You have the classic arithmetic overflow bug in your computation of mid

Here is corrected version:

int binSearch(int arr[], int size, int target, int *numComparisons) {
    int first = 0;
    int last = size;
    int comp = 0;

    while (first < last) {
        int mid = first + (last - first) / 2;

        comp++;
        if (arr[mid] == target) {
            *numComparisons = comp;
            return mid;
        }
        comp++;
        if (arr[mid] < target) {
            first = mid + 1;
        } else {
            last = mid;
        }
    }
    *numComparisons = comp;
    return -1;   
}