I have a struct:
typedef struct
{
int nNum;
string str;
}KeyPair;
Let's say I initialize my struct:
KeyPair keys[] =
{ {0, "tester"},
{2, "yadah"},
{0, "tester"}
};
I want to use the initialized values in a function. How do I pass this array struct as a function parameter?
I have:
FetchKeys( KeyPair *pKeys)
{
//get the contents of keys[] here...
}
How about?
template<int N> void FetchKeys(KeyPair const (&r)[N]){}
EDIT 2:
Or even
template<int N> void FetchKeys(KeyPair const (*p)[N])
with the call as
FetchKeys(&keys);
You can do it as @MSalters mentioned, or you can create a std::vector<KeyPair>
and pass it to the function. Here is a sample code:
using namespace std;
struct KeyPair
{
int nNum;
string str;
};
void fetchKeys(const vector<KeyPair>& keys)
{
//Go through elements of the vector
vector<KeyPair>::const_iterator iter = keys.begin();
for(; iter != keys.end(); ++iter)
{
const KeyPair& pair = *iter;
}
}
int main()
{
KeyPair keys[] = {{0, "tester"},
{2, "yadah"},
{0, "tester"}
};
//Create a vector out of the array you are having
vector<KeyPair> v(keys, keys + sizeof(keys)/sizeof(keys[0]));
//Pass this vector to the function. This is safe as vector knows
//how many element it contains
fetchKeys(v);
return 0;
}
Should be
// Definition
void FetchKeys( KeyPair *pKeys, int nKeys)
{
//get the contents of keys[] here...
}
// Call
FetchKeys(keys, sizeof(keys)/sizeof(keys[0]));
You just call FetchKeys(keys);
EDIT
Pay attention to declare FetchKeys
' return type.
EDIT 2
If you also need the number of items, you add size as FetchKeys
input parameters:
void FetchKeys(KeyPair*, size_t size);
and call FetchKeys(keys, sizeof(keys)/sizeof(*keys));
BTW, state all your question by editing your first post if you can.
In c/c++ the name of the array (of any type) represents the address of the first element of the array, so keys and &keys [0] are same. You can pass any one of them for KeyPair*.
Depending on what you want to do you can even use boost range and pass it to function as a pair of iterators:
void FetchKeys(KeyPair *begin, KeyPair *end)
FetchKeys(boost::begin(keys), boost::end(keys));
See this answer: How can I pass an array by reference to a function in C++?
Wrap it in a structure, nice and easy..
#include <iostream>
struct foo
{
int a;
int b;
};
template <typename _T, size_t _size>
struct array_of
{
static size_t size() { return _size; }
_T data[_size];
};
template <typename _at>
void test(_at & array)
{
cout << "size: " << _at::size() << std::endl;
}
int main(void)
{
array_of<foo, 3> a = {{ {1,2}, {2,2}, {3,2} }};
test(a);
}
EDIT: URGH, I can't see the toolbar to format the code correctly, hopefully the tags works..
i use VS 2008, and this works fine for me.
#include "stdafx.h"
typedef struct
{
int nNum;
CString str;
}KeyPair;
void FetchKeys( KeyPair *pKeys);
int _tmain(int argc, _TCHAR* argv[])
{
KeyPair keys[] =
{ {0, _T("tester")},
{2, _T("yadah")},
{0, _T("tester")}
};
FetchKeys(keys); //--> just pass the initialized variable.
return 0;
}
void FetchKeys(KeyPair *pKeys)
{
printf("%d, %s\n",pKeys[0].nNum, pKeys[0].str);
}
I don't understand the difficulty. correct me if i'm wrong. To keep it simple, i avoided using vectors, templates and etc. edit: to know size of struct, you can pass one more arg.
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