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Polynomial
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DoomsDay
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 Posted: Fri Aug 21, 2009 3:04 pm Post subject: |
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| You should return a pointer.
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Polynomial
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| Posted: Fri Aug 21, 2009 3:30 pm Post subject: |
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A pointer to what data type?
I've tried byte** and I couldn't get it to work.
Update: Fixed it by using a single dimension array and messing with the array index with mathematical stuff. Pleh.
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Stylo
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| Posted: Fri Aug 21, 2009 5:03 pm Post subject: |
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it depends on the array type ...
for int you should return int*
the pointer that will be returned is the start address of the array
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hcavolsdsadgadsg
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| Posted: Sat Aug 22, 2009 4:01 am Post subject: |
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Just pass the array, it's pointing to the first element on its own, go wild.
| Code: | #include <Windows.h>
//////////////////////////////////////////////////////////////////////////
void cool_func(void* in_arr, void* out_arr)
{
memcpy(out_arr, in_arr, 4 * 64);
}
//////////////////////////////////////////////////////////////////////////
int __cdecl main(void)
{
int i;
int butt[64];
int dong[8][8];
for(i = 0; i < 64; i++)
butt[i] = i;
cool_func((int*)butt, (int*)dong);
return 0;
} |
You can also just return a pointer to the array, but you'll need to allocate some memory on the heap and point to that as since when the function returns, your array on the stack is toast. Just remember to free the memory after.
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Jani
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| Posted: Sat Aug 22, 2009 6:34 am Post subject: Re: Returning array in C++ |
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| Burningmace wrote: | | and even vector<vector<byte>>. |
| Code: | #include <iostream>
#include <vector>
#include <iomanip>
#include <cstdlib>
#include <ctime>
typedef unsigned char byte;
std::vector< std::vector< byte > > f(byte x[])
{
std::vector< std::vector< byte > > v;
for(int i=0; i<8; ++i) {
std::vector<byte> b;
for(int j=0; j<8; ++j)
b.push_back( x[i*8+j] );
v.push_back( b );
}
return v;
}
int main(int argc, char*argv[])
{
byte a[64] = { 0 };
srand( static_cast< unsigned int >( time(NULL) ) );
for(int i=0; i<64; ++i)
a[i] = static_cast< byte >( (static_cast< double >(rand()) / RAND_MAX )*0xFF );
std::cout << "a[64]:" << std::endl;
for(int i=0; i<8; ++i) {
for(int j=0; j<8; ++j)
std::cout << std::setw(3) << static_cast< int >( a[i*8+j] ) << " ";
std::cout << std::endl;
}
std::cout << std::endl;
std::vector< std::vector< byte > > v;
std::vector< std::vector< byte > >::iterator vitr;
std::vector< byte >::iterator bitr;
v = f(a);
std::cout << "v:" << std::endl;
for(vitr = v.begin(); vitr != v.end(); ++vitr) {
for(bitr = vitr->begin(); bitr != vitr->end(); ++bitr)
std::cout << std::setw(3) << static_cast< int >(*bitr) << " ";
std::cout << std::endl;
}
std::cout << std::endl;
std::cout << "a[i*8+j] == v.at(i).at(j):" << std::endl;
for(int i=0; i<8; ++i) {
for(int j=0; j<8; ++j)
std::cout << ( a[i*8+j] == v.at(i).at(j) ) << " ";
std::cout << std::endl;
}
return EXIT_SUCCESS;
} |
Note that sizeof(x) is 4 on 32-bit machines. So, you must make sure that it's really a 64 byte array before calling the function.
EDIT: oh right, forgot to do stuff with byte x[].
EDIT2: yeah, right, forgot to reply the original question: if you want to return an array, you can't. Try this: | Code: | typedef byte byteArray[2];
byteArray function()
{ byteArray a; return a; } |
and you'll get an error like: | Code: | | error C2090: function returns array |
Solution: use classes or pointers. Also, you could pass the output array as a param, but that's not really returning..: | Code: | #include <iostream>
#include <iomanip>
#include <ctime>
#include <cstdlib>
typedef unsigned char byte;
void f(byte x[], byte y[8][8])
{
for(int i=0; i<8; ++i) {
for(int j=0; j<8; ++j)
y[i][j] = x[i*8+j];
}
return;
}
int main(int argc, char *argv[])
{
byte a[64] = { 0 };
byte b[8][8] = { 0 };
srand( static_cast< unsigned int >( time(NULL) ) );
for(int i=0; i<64; ++i)
a[i] = static_cast< byte >( (static_cast< double >(rand()) / RAND_MAX )*0xFF );
std::cout << "b[8][8]:" << std::endl;
for(int i=0; i<8; ++i) {
for(int j=0; j<8; ++j)
std::cout << std::setw(3) << static_cast< int >( b[i][j] ) << " ";
std::cout << std::endl;
}
std::cout << std::endl;
f(a, b);
std::cout << "b[8][8]:" << std::endl;
for(int i=0; i<8; ++i) {
for(int j=0; j<8; ++j)
std::cout << std::setw(3) << static_cast< int >( b[i][j] ) << " ";
std::cout << std::endl;
}
std::cout << std::endl;
return EXIT_SUCCESS;
} |
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