# V783\. Possible dereference of invalid iterator 'X'\.

The analyzer detected a code fragment that may result in using an invalid iterator\.

Consider the following examples that trigger this diagnostic message:

```cpp
if (iter != vec.end() || *iter == 42) { ... }
if (iter == vec.end() && *iter == 42) { ... }
```

There is a logic error in all the conditions above that leads to dereferencing an invalid iterator\. This error usually appears during code refactoring or because of a typo\.

The fixed versions:

```cpp
if (iter != vec.end() && *iter == 42) { ... }
if (iter == vec.end() || *iter == 42) { ... }
```

Of course, these are very simple cases\. In practice, the check and the code using the iterator are often found in different lines\. If you got the V783 warning, check the code above and try to find out why what made the analyzer treat the iterator as invalid\.

Here is an example where the iterator is checked and used in different lines:

```cpp
if (iter == vec.end()) {
  std::cout << "Error: " << *iter << std::endl;
  throw std::runtime_error("foo");
}
```

The analyzer will warn you about the issue in the '\*iter' expression\. Either it is an incorrect condition or some other variable should be used instead of 'iter'\.

The analyzer can also detect cases when the iterator is used before being checked\.

Consider the following example:

```cpp
std::cout << "Element is " << *iter << std::endl;
if (iter == vec.end()) {
  throw std::runtime_error("");
}
```

The check here is meaningless because the possibly invalid iterator has been already dereferenced\. There is a missing check:

```cpp
if (iter != vec.end()) {
  std::cout << "Element is " << *iter << std::endl;
}
if (iter == vec.end()) {
  throw std::runtime_error("");
}
```