当大小为零时，hash_map在第一次查找期间崩溃

Question

I am new to hash_map in c++. I have to convert a table in to hashmap.

This is how I have declared and using hash_map in my program

I am using microsoft visual studio.

#include <hash_map>
using namespace stdext;
typedef hash_multimap <const char*, long > HEAPTABLE;

typedef HEAPTABLE::iterator HEAP_ITER;

class CTest
{

public:

 void setSwitchID(long i);
 long getSwitchID();
 void isUpgrading(bool bTest);
private:

 HEAPTABLE m_hashMap;
};

void CTest::setSwitchID(long dwID)
{


 HEAP_ITER hIter = m_hashMap.find("SwitchId");
 if (hIter != m_hashMap.end())
 {
  hIter->second = dwID;
 }
 else
 {
  m_hashMap.insert(make_pair("SwitchId", dwID));
 }

}

long CTest::getSwitchID()
{

 HEAP_ITER hIter = m_hashMap.find("SwitchId");
 if (hIter != m_hashMap.end())
 {
  return hIter->second;
 }
 return 0;

}

int _tmain(int argc, _TCHAR* argv[])
{

  CTest* test = new CTest;
          if (test)
          {

  test->setSwitchID((DWORD)i);
  test->isUpgrading(false);
         }
 delete test;
 return 0;

}

This code works fine when I run it as a separate program but when I try run it as part of my project the application crashes. Even if there are no entry in the map the hIter in the set function is returning bad pointer. Is this because of memeory corruption? Could you please help?

If it is a heap corruption, how can i avoid this? Is there anyway I can say create a hash_map with this size?

Answer 1

hash_multimap <const char*, long > does not do what you think it does. The key is a pointer not a string. Your small program works by luck of compiler using the same memory for both "SwitchId" string literals. This is not the case in a larger project.

Use std::string as a key instead and, while here, switch to std::unordered_multimap .