Walking thru a STL list and remove element at the same time?

[Allerdyce.John]

In STL list, is it safe to do this:

list<A> aList; //private attribute of MyClass


void MyClass:: aMethod() {
list<A>::Iterator iter;

for ( iter = aList.begin() ; iter != aList.end() ; iter++) {
A a = (*iter);

if ( check(a) ) {

aList.erase (iter); // is that okay?

}
}

}

Thank you.

 

[roberts.noah]

In STL list, is it safe to do this:

list<A> aList; //private attribute of MyClass


void MyClass:: aMethod() {
list<A>::Iterator iter;

for ( iter = aList.begin() ; iter != aList.end() ; iter++) {
A a = (*iter);

if ( check(a) ) {

aList.erase (iter); // is that okay?

Change to iter = aList.erase(iter);

 

[roberts.noah]

Change to iter = aList.erase(iter);

Oh, and of course you will only want to increment iter if you don't
delete.

 

[E. Mark Ping]

Change to iter = aList.erase(iter);

Which will get you into trouble when you get to iter++ at the for
loop.

The full approach is:

list<A> aList; //private attribute of MyClass

void MyClass:: aMethod() {
list<A>::Iterator iter;

//note no increment in the third clause of the for loop
for ( iter = aList.begin() ; iter != aList.end() ; ) {
A a = (*iter);

if ( check(a) ) {
iter = aList.erase (iter); // is that okay?
} else {
++iter;
}
}

}


Or you can simply use remove_if.

 

[Daniel T.]

In STL list, is it safe to do this:

list<A> aList; //private attribute of MyClass


void MyClass:: aMethod() {
list<A>::Iterator iter;

for ( iter = aList.begin() ; iter != aList.end() ;
iter++) {
A a = (*iter);

if ( check(a) ) {

aList.erase (iter); // is that okay?

}
}

}

Thank you.

aList.erase(aList.begin(),
remove_if(aList.begin(), aList.end(), &check ));

But don't do the above if aList contains pointers and you need to delete
the objects before removal. Of course, if that's the case then you
should probably wrap them in a smart pointer.

 

[Richard Herring]

aList.erase(aList.begin(),
remove_if(aList.begin(), aList.end(), &check ));

The remove_if algorithm may have to copy many instances of A, which
could potentially be quite expensive. std::list provides a more
efficient alternative:

aList.remove_if(check);