please can you help me? How can I copy part of one int array to another int array?
Example:
typedef struct part {
int * array;
} PART;
int array[] = {1,2,3,4,5,6,7,8,9};
PART out[] = new PART[3];
for (int i = 0; i < 3; i++)
{
memcpy((char *)array[i * 3], (char *)out[i].array, 3 * sizeof(int));
}
But this don't working... :(
Ok you have 3 problems.
You are casting an int to a char* (char *)array[i * 3]
What you really mean is (char *)&array[i * 3]. ie take the address of the i*3th element.
you are trying to copy data from an uninitialised array.
you should allocate memory to out[i].array.
You appear to have your memcpy the wrong way round.
The following code will work better:
typedef struct part {
int * array;
} PART;
int array[] = {1,2,3,4,5,6,7,8,9};
PART out[] = new PART[3];
for (int i = 0; i < 3; i++)
{
out[i].array = new int[3];
memcpy( (char *)out[i].array, (char *)&array[i * 3], 3 * sizeof(int));
}
Make sure you remember to delete[] the memory allocated to out[i].array ...
You need to allocate memory for * array before doing memcpy.
Something like this:
typedef struct part {
int * array;
} PART;
int array[] = {1,2,3,4,5,6,7,8,9};
PART out[] = new PART[3];
for (int i = 0; i < 3; i++)
{
out[i].array = malloc(9*sizeof(int));
// will copy 9 array values into out[i].array
memcpy(out[i].array, array, 9 * sizeof(int));
}
int *array inside that struct is uninitialized. It must be initialized.
int s in each PART.
PART?The struct part of this is kind of irrelevant. What you are trying to do can be accomplished this way:
int src[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
int part[3][3];
for (int i = 0; i < 3; ++i)
{
std::copy(src + (3 * i), src + (3 * (i + 1)), part[i]);
}
An even better solution can be done by using std::vector instead of C-style arrays:
std::vector<int> a(src, src + 9);
std::vector<std::vector<int> > b;
for (int i = 0; i < 3; ++i)
{
std::vector<int> c(a.begin() + (3 * i), a.begin() + (3 * (i + 1)));
b.push_back(c);
}
memcpyis probably wrong. the first argument ofmemcpyis the destination, not the source.