vector :: clear（）导致段错误

Question

I have a std::vector that is causing some very strange seg faults

//A.h
class A{
private:
  std::vector<float> data;
public:
  void set(const std::vector<float>& data);
};
//A.cpp
void A::set(const vector<float>& data){
  this->data.clear(); // crashes on this line
  for(float f : data) this->data.push_back(f);
}

Under what possible circumstances could vector::clear() cause a seg fault? I initially had

void A::set(const vector<float>& data){
  this->data = data;
}

and had the same problem. I switched to the above to debug. This is on gcc 4.7.2, x86_64

Answer 1

IF it crashes precisely at the call to 'data.clear' (I mean, at exactly this line, not somewhere inside the clear), then be sure to check your this pointer at the faulting line.

If somehow your $this is null or trash-value due to accumulated effects of previous bugs, then this line might behave similarily.

On the (almost) other hand, if it actually crashes somewhere inside the clear and you just have cut the stacktrace to make the problem description more succint, then still it is possible to be the same cause.

You may check the 'this' pointer for NULL easily in the debugger. Also, detecting trashvalues is not hard: add some testfields to the A class, fill them in constructor with some predictable BUT NOT CONSTANT values, and when the app crashes, check if the this->mytestvalue is ok. If the $this is trashed, then the pointed test values will very often be almost random.

Answer 2

Likely this is due to stack/memory corruption occurring somewhere else. You should run your program with a memory checker, such as Valgrind using the memcheck tool to see what's going on.