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Having assertion failure while deleting an element from a vector.What are the causes of assertion failure?

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Dani AI

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A few focused points to clarify the failure and give safe alternatives.

The assertion is most likely caused by iterator invalidation: erasing an element from a std::vector while also advancing the same iterator leads to undefined behavior and triggers debug assertions. noted the iterator-return behavior of erase — that is the core issue here — but ownership and lifetime problems (double-delete, dangling pointers, deleting objects not allocated with new) can produce the same symptom. ’s hint about memory corruption is also relevant: a corrupted heap or overrunning buffers elsewhere in the program will make vector operations fail later.

Safer, modern option: stop using raw owning pointers and let RAII handle deletion. Convert vector<x*> to vector<std::unique_ptr<x>> and use erase + remove_if:

std::vector<std::unique_ptr<X>> v;
// remove elements that match some predicate
v.erase(std::remove_if(v.begin(), v.end(),
    [](const std::unique_ptr<X>& p){ return should_remove(p.get()); }),
    v.end());

This removes manual delete and is exception-safe.

If raw pointers must be used, iterate from back to front to avoid invalidating indices of remaining elements:

for (size_t i = v.size(); i-- > 0; ) {
    if (should_remove(v[i])) {
        delete v[i];
        v.erase(v.begin() + i);
    }
}

This keeps earlier indexes stable and avoids the "erase then ++iter" pitfall.

Practical debugging checklist (in order): run with AddressSanitizer or Valgrind to catch buffer overruns and double-free; enable your toolchain’s debug heap checks (MSVC debug runtime); verify every pointer you delete is owned once and was allocated with new; ensure base classes have virtual destructors if deleting through base pointers; and add assertions/logging around allocations and deletes to find double-deletes. Refer back to and for pointer-content checks and ownership strategy.

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Member Avatar for Ancient Dragon

Lots of different causes, one being your program may have scribbled something all over memory and damaged vector's memory space. Another problem could be bad use of pointers. Without knowing more details about the program its not possible to give you any really good answers to your question.

One way to debug the program is to start commenting out sections of the code until the assertion failure goes away. That will let you narrow down the problem.

Edited by Ancient Dragon because: n/a
Member Avatar for sita12345

Hello Thankyou.Below is my code.In the x.erase(iter) i am getting that problem

        vector<x*>::iterator iter;
    for(iter=x.begin();iter!=x.end();++iter)
    {
        delete *iter;
        x.erase(iter);
    }

I debugged but couldn't understand what is the exact problem?

Edited by Nick Evan because: Fixed formatting
Member Avatar for mrnutty

Are you trying to delete a vector of pointers?

std::vector<x*>::iterator begin = x.begin();

while(!x.empty()){
 x* tmp = x.back();
 x.pop_back();
 delete tmp;
}
x.clear();
Member Avatar for vijayan121

There is a problem with this code:

vector<x*>::iterator iter;
 for(iter=x.begin();iter!=x.end();++iter)
 {
     delete *iter;
     x.erase(iter); // once the element is erased, the iterator is no longer valid
     // ++iter now will cause undefined behaviour. 
 }

Instead, you could use the value returned by erase:

vector<x*>::iterator iter;
 for( iter=x.begin() ; iter!=x.end() ; iter = x.erase(iter) )
 {
     delete *iter;
 }

This is perhaps the simplest way to do it:

for( auto ptr : x ) delete ptr ;
x.clear() ;
Edited by vijayan121 because: n/a
Member Avatar for sita12345

Hi,
I dont want the entire vector to be cleared.I need only few elements to be deleted from a vector.By doing clear all my elements are getting erased?
Vijayan i tried ur code even then it is throwing assertion failure.

Member Avatar for mrnutty

Make sure what you are deleting is something that should be deleted!. Anyways, the key point to take is that vector::erase returns a iterator pointing to the next element after the one deleted. If possible, put up the whole context(i.e full code )

Edited by mrnutty because: n/a
Member Avatar for raptr_dflo

Among other things, you may have NULL pointers in your vector, which can't be delete d. Verify what's in your vector before you worry about what's wrong with your deletion code, e.g.:

// changed to while() loop to make logic more obvious
vector<T*>::iterator iter = x.begin();
while (iter != x.end()) {
    T* ptr = *iter;
    if (! ptr) {
        // NULL pointer in your vector
    }
    else if ( /* test to see if element should be removed */ ) {
        delete ptr;
        iter = x.erase(iter);
    }
    else
        iter++;
}
Member Avatar for mrnutty

Among other things, you may have NULL pointers in your vector, which can't be delete d. Verify what's in your vector before you worry about what's wrong with your deletion code, e.g.:

// changed to while() loop to make logic more obvious
vector<T*>::iterator iter = x.begin();
while (iter != x.end()) {
    T* ptr = *iter;
    if (! ptr) {
        // NULL pointer in your vector
    }
    else if ( /* test to see if element should be removed */ ) {
        delete ptr;
        iter = x.erase(iter);
    }
    else
        iter++;
}

its perfectly fine to delete a null pointer

Member Avatar for raptr_dflo

its perfectly fine to delete a null pointer

Lucky me! This is what I get for starting with C programming, and then learning C++ later ... I'm way too careful about handling pointers! And yes, I'm old enough to pre-date a usable C++ compiler.

Member Avatar for sita12345

Thanks to everyone for suggestions.

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