So my question is pretty simple, tho I haven't been able to find an answer already so I'm asking here.
I curious to know whether I can return an std:: pair reference from a function, and have the calling function modify its values. Here's an example of what I mean:
struct PairStruct {
using PairType = std::pair<size_t, size_t>;
PairStruct() : m_pair(std::make_pair(0, 0)) {}
void modifyInternal() {
auto pair = getPair();
std::cout << "start - first: " << pair.first << ", second: " << pair.second << "\n";
pair.first++;
pair.second++;
std::cout << "end - first: " << pair.first << ", second: " << pair.second << "\n";
}
void modifyPtrInternal() {
auto pair = getPairPtr();
std::cout << "start - first: " << pair->first << ", second: " << pair->second << "\n";
pair->first++;
pair->second++;
std::cout << "end - first: " << pair->first << ", second: " << pair->second << "\n";
}
PairType &getPair() {
return m_pair;
}
PairType *getPairPtr() {
return &m_pair;
}
PairType m_pair;
};
int main(int argc, char ** args)
{
PairStruct *pairInst = new PairStruct;
// Test with reference
std::cout << "Reference test.\n";
pairInst->modifyInternal();
std::cout << "\n";
pairInst->modifyInternal();
std::cout << "\n";
// Test with ptr
std::cout << "Ptr test.\n";
pairInst->modifyPtrInternal();
std::cout << "\n";
pairInst->modifyPtrInternal();
delete pairInst;
return 0;
}
As expected when I use a pointer it correctly modyfies the values, this is not the case when returning a reference. Here's the output of this program:
Reference test.
start - first: 0, second: 0
end - first: 1, second: 1
start - first: 0, second: 0
end - first: 1, second: 1
Ptr test.
start - first: 0, second: 0
end - first: 1, second: 1
start - first: 1, second: 1
end - first: 2, second: 2
This is going to seem very trivial, however, I'd like to know why I can't use the referenced pair in this case. Thanks!
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