CODEWITHSUNDEEP
c++vector
user1558064
user1558064

Reputation: 887

questions regarding to vector reserve large memory

If I reserve large amount of memory for a vector, (it will be filled out with data later on), can the memory reserved be used by others?

for example, 

vector<double* > vD;
vD.reserve(30000000);  // the number is less than the maximum size of a vector

... ...
for(int i=0; i< 1000000; i++)
{
    double * pF = new double;  // will be pushed back to the vector

    ... ...
    vD.push_back(pF);

    delete pF;
}
pF = NULL;

The code above just shows the idea. In the real code, double is an self-defined object which contains pointers. When I run the code, I got crashed with info: Free heap block 3bab8 modified at 3bacc after it was freed. The exact memory address(3bab8 and 3bacc ) will change. when I checked my vector: 

for _First --- 0x28df0020
    _Last      0x28df0870
    _End       0x3ece3c20

For my understanding, the memory reserved for vD should go btw 0x28df0020 and 0x3ece3c20. If I understand this right, then the memory reserved is untouched. Am I right? Then why do I get heap block modified after it was freed? How should I deal with it? Thanks.

Upvotes: 0

Views: 98

Answers (1)

Benjamin Lindley
Benjamin Lindley

Reputation: 103703

You're storing pointers to objects, then deleting those objects, thereby invalidating the pointers. The solution is to simply store objects, not pointers to objects.

vector<double> vD;
...
double pF;
...
vD.push_back(pF);

For cases where you must use pointers (e.g. polymorphic objects), use smart pointers.

vector<unique_ptr<Base>> vD;
...
unique_ptr<Base> pF(new Derived);
...
vD.push_back(move(pF));

The queries about reserve are irrelevant to your problem, but to answer your question: No, once you've reserved space for your vector, others may not use it.

Upvotes: 2

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