如何将 C 中的两个整数数组与 for 循环合并

Question

I am trying to merge two arrays but there seems to be a problem. I try to use a simple loop but it doesn't work. My first problem is that I don't know how to stop the for loop for an array, and the second is that every time it assigns some garbage value to the merged array. If someone could just give me a direction…

int arr1[] = {1,2,3,4,5,0}, arr2[] = {6,7,8,9,0};

int x = 0, merge_arr[x], i = 0, x1 = 0;

for( ; arr1[i] != 0; i++)
{
    merge_arr[i] = arr1[i];
    printf("%di ", merge_arr[i]);
}

for( ; arr2[x1] != 0; i++)
{
    merge_arr[i] = arr2[x1];
    printf(" %di ", merge_arr[i]);
    x1++;
}

for(int x2 = 0; merge_arr[x2] != '\0'; x2++)
{
    printf("%d\n", merge_arr[x2]);
}

Answer 1

As C is a procedural language, it is good to define functions for such operations. C standard provides a special type size_t for the sizes.

int *concatIntArrays(int *dest, size_t maxSize, const int *arr1, const size_t arr1Size, const int *arr2, const size_t arr2Size)
{
    size_t toCopy;
    if(!dest)
    {
        dest = malloc(maxSize ? maxSize * sizeof(*dest) : (maxSize = (arr1Size + arr2Size)) * sizeof(*dest));
    }
    if(dest)
    {
        if(arr1Size <= maxSize) toCopy = arr1Size;
        else toCopy = maxSize;
        memcpy(dest, arr1, toCopy * sizeof(*dest));

        maxSize -= toCopy;

        if(arr2Size <= maxSize) toCopy = arr2Size;
        else toCopy = maxSize;
        memcpy(dest + arr1Size, arr2, toCopy * sizeof(*dest));
    }
    return dest;
}

or more generic one:

void *concatArrays(void *dest, const size_t elemSize, size_t maxSize, const void *arr1, const size_t arr1Size, const void *arr2, const size_t arr2Size)
{
    size_t toCopy;
    char *tempdest = dest;
    if(!dest)
    {
        dest = malloc(maxSize ? maxSize * elemSize : (maxSize = (arr1Size + arr2Size)) * elemSize);
    }
    if(dest)
    {
        if(arr1Size <= maxSize) toCopy = arr1Size;
        else toCopy = maxSize;
        memcpy(dest, arr1, toCopy * elemSize);

        maxSize -= toCopy;

        if(arr2Size <= maxSize) toCopy = arr2Size;
        else toCopy = maxSize;
        memcpy(tempdest + arr1Size * elemSize, arr2, toCopy * elemsize);
    }
    return dest;
}

where all sizes are in the elements. elemSize in bytes.

You can pass your own buffer (destination array) or NULL - then the function will allocate it for you. If the maxSize is zero it allocates as much memory as needed to accommodate both arrays.