为什么在C中此程序存在分段错误错误？

Question

Why is dr segmentation fault in this code? Everything look correct here, syntax ... etc.The program is simple,just two sort content of two arrays into a third array; So I have taken two arrays array1 and array2 and the third one is array in which sorting is to be done.

#include<stdio.h> 

int main()
{
    int array1[10] = {1, 2, 4,5,7,8,45,21,78,25};
    int array2[5] = {3, 6, 9,15,17};
    int array[20];
    int i,j,temp;
    int l1 = sizeof(array1)/sizeof(int);
    int l2 = sizeof(array2)/sizeof(int);
    int l3 = l1+l3;

    for (i = 0;i < l1; i++) 
    {
        array[i]=array1[i];
    }
    for (i = 0;i < l2; i++) 
    {
        array[i+l1]=array2[i];
    }
    for (i = 0;i < (l1+l2); i++) 
    {
        printf("%d\n", array[i]);
    }
    printf("\nSorted array:\n");

    for(i=0;i<l3;i++)
    {
        for(j=i;j<l3;j++)
        {
            if(array[i] > array[j])
            {
                temp=array[i];
                array[i]=array[j];
                array[j]=temp;
            }
        }
    }
    for (i = 0;i < l3; i++) 
    {
        printf("%d\n", array[i]);
    }

    return 0;
}

Answer 1

Because this is not what you want:

int l3 = l1 + l3;

It will simply add the known l1 to the arbitrary l3 , giving you a slightly larger arbitrary value. Instead, it should be:

int l3 = l1 + l2;

---

The other, though relatively minor, problem you have is the efficiency of the algorithm, specifically the start and end conditions of the loops. The code:

for (i = 0; i < l3; i++) {
    for (j = i; j < l3; j++) {

has two problems. First, the i loop goes too far since we know that when it's at l3 - 1 , there are no elements to the right. Secondly, the j loop starts at i and we know that array[x] > array[x] can never be true ( x because i == j ).

It would be better to use:

for (i = 0; i < l3 - 1; i++) {
    for (j = i + 1; j < l3; j++) {

to remove these inefficiencies.

Answer 2

In the line:

// l3 will have garbage value which might be a greater than 20(max size of your array)

int l3 = l1+l3;

When you are using this in the loops

for(i=0;i<l3;i++)
{
    for(j=i;j<l3;j++)
    {
        if(array[i] > array[j])
        {
            temp=array[i];
            array[i]=array[j];
            array[j]=temp;
        }
    }
}
for (i = 0;i < l3; i++) 
{
    printf("%d\n", array[i]);
}

l3 value may be more than 20 say 30 when accessing the 30th location of the array will lead to segmentation fault.

Answer 3

Because you are exceeded the size of array

check this instruction: int I3 = I1+I3 you should replace it by int I3 = I1+I2