Erasing Map Location Causes Error

[Studlyami]

Hey guys i have a map Which links vectors to each other. I have a loop and during the loop i want to delete a position in the map, but every time i do the iterator becomes null and causes an error. My code is below (well a frame of it)

MyMap <CString, int>
MyMap::iterator MapIterator;

 
    bool TestBool = false;
    for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); ++MapIterator)
    {
        for(int j = 0; j<MyVector.size(); j++)
        {
           int StrCmpResult = strcmp((*MapIterator).first, MyVector[j].String); 
            if(StrCmpResult == 0)
            {
                TestBool = true;
               break;
            }
        }
 
        if(TestBool==false)
        {          
               MyMap.erase(MapIterator);
        }
   }
 

When it hits MyMap.erase(MapIterator) it does the map erase, but then when it hits the next iteration of the for loop MapIterator = null. How can i delte an item out of the map during the loop?

[Savage]

Hey guys i have a map Which links vectors to each other. I have a loop and during the loop i want to delete a position in the map, but every time i do the iterator becomes null and causes an error. My code is below (well a frame of it)

MyMap <CString, int>
MyMap::iterator MapIterator;

 
    bool TestBool = false;
    for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); ++MapIterator)
    {
        for(int j = 0; j<MyVector.size(); j++)
        {
           int StrCmpResult = strcmp((*MapIterator).first, MyVector[j].String); 
            if(StrCmpResult == 0)
            {
                TestBool = true;
               break;
            }
        }
 
        if(TestBool==false)
        {          
               MyMap.erase(MapIterator);
        }
   }
 

When it hits MyMap.erase(MapIterator) it does the map erase, but then when it hits the next iteration of the for loop MapIterator = null. How can i delte an item out of the map during the loop?

You need to "reset" your map iterator after you delete a value which it has pointed to.

Savage

[Banfa]

When it hits MyMap.erase(MapIterator) it does the map erase, but then when it hits the next iteration of the for loop MapIterator = null. How can i delte an item out of the map during the loop?

The erase method returns the correct value of the iterator to continue the loop, this means you have to selectively decide how to obtain the next iterator value something like

 
    for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); )
    {
        <snipped>
 
        if(TestBool==false)
        {          
               MapIterator = MyMap.erase(MapIterator);
        }
        else
        {          
               ++MapIterator;
        }
   }
 

[Studlyami]

      for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); )
          {
              if(TestBool==false)
              {         
                     MapIterator = MyMap.erase(MapIterator);
              }
              else
              {         
                     ++MapIterator;
              }
         }
 

I tried this and it still doesn't work. It hits the string compare and i get a memory access violation.

As for trying to reset my iterator how exactly would i go about doing this? i tried the code down below, but it doesn't like MapIterator = MyMap.begin() + <int>;

int i = 0;
      for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); ++MapIterator)
          {
              if(TestBool==false)
              {         
                     MapIterator = MyMap.erase(MapIterator); 
                     MapIterator = MyMap.begin() + i;
              }
          i++;
         }
 

[Savage]

I tried this and it still doesn't work. It hits the string compare and i get a memory access violation.

As for trying to reset my iterator how exactly would i go about doing this? i tried the code down below, but it doesn't like MapIterator = MyMap.begin() + <int>;

int i = 0;
      for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); ++MapIterator)
          {
              if(TestBool==false)
              {         
                     MapIterator = MyMap.erase(MapIterator); 
                     MapIterator = MyMap.begin() + i;
              }
          i++;
         }
 

Probably because map iterator is bidirectional so it doesn't behave as a "dumb" pointer which means that it doesn't support it's arithmetic.You should be able to do this like:

i=0;
for(MapIterator = MyMap.begin(); MapIterator != MyMap.end(); ++MapIterator)
{
              if(TestBool==false)
              {         
                     MapIterator = MyMap.erase(MapIterator); 
                     for(int pos=0;pos<i;pos++) ++MapIterator;
 
 
              }
              i++;
 
 
}

Savage

[Studlyami]

Thanks, That code worked great. I needed to do pos<i-1; in the for loop and it works perfectly.

[Savage]

Thanks, That code worked great. I needed to do pos<i-1; in the for loop and it works perfectly.

I'm more then happy to help you.

Oh,and you wasted some valuable time(time is money) figuring out pos<i-1,please forgive me for my nonsense,I was tired.

Savage