向量迭代器不可增量 [英] vector iterator not incrementable

问题描述

* 编辑：我移除了else部分。迭代器已重复两次*

运行时出错：

文件：c：\program files（x86）\microsoft visual studio 10.0 \vc\include\vector
行：99

表达式：向量迭代器不可递增

---

文件：c：\program files（x86）\microsoft visual studio
10.0 \vc\include\vector行：100

表达式：标准C ++库超出范围&& 0

我的代码必须在目录中找到新图片时发送警报。但是由于我不能自己删除文件，我不得不骗。在发现图像时发送报警之前，我将其与已发送的图像（sentPictures）进行比较。在sentPictures中，我删除了在目录中删除的图像，因为如果我必须比较每一次在过去发现的每一个图像，该程序可能有点重xD
（它在一个无限循环） / p>

这是我得到的错误。要找到存储的元素是否仍然在目录中，我将旧元素vector（sentPictures）与新的元素（refreshVector）进行比较。对于每个旧元素（sentPictures），如果他们没有在refreshVector中找到，我删除它们一个一个。在我的情况下，我得到的错误，即使没有做。只是走过这个循环崩溃。在我的情况下，我有9个元素在目录中，它打印5和崩溃。我检查，有作为nuch元素在sentPictures然后在refreshVector。我想我不能很好地处理迭代器的使用。这是代码片。

  for（std :: vector< Picture> :: iterator it = sentPictures.begin ; it！= sentPictures.end（）; it ++）{
 std :: cout< 1<< std :: endl; 
 
 if（std :: find（refreshVector.begin（），refreshVector.end（），* it）== refreshVector.end（））{
 tcout< * it<< std :: endl; 
 //如果在刷新向量中找不到图片，则删除它
 // delete * it; 
 // it = refreshVector.erase（it）; 
} else {
 std :: cout<< 2<<< std :: endl; 
 ++ it; 
} 
 
} 
  

PS：指令删除* ;不编译。 VS说表达式必须有指针或句柄类型，基础*符号。我将搜索是否不是关于事实it用于if条件。

解决方案

指令delete * it;不会编译。

您正在尝试删除一个对象，delete需要一个指针。你也不应该删除/删除[]任何东西没有分配使用新/新[]，这似乎你不是，因为你有一个对象（不是指针）的向量。

如果你想从一个容器中删除sth，你应该使用它相应的函数 vector< T> :: erase（）。 delete 仅适用于在堆上分配的对象。

使用迭代器可以安全地使用索引。

  for（int i = 0; i！= sentPictures.size ; i ++）
 {
 sentPictures [i]; // 
 // etc 
} 
  

一个迭代器。

另一个注意事项，不要后递增迭代器，它会做一个冗余副本，预先递增它，虽然不知道编译器将会优化。

现在擦除问题似乎被裁决，我需要通过这个
代码，直到它结束。它崩溃在lopp的某个地方，但不知道
为什么。

它崩溃，因为你正在擦除循环;在删除元素时会更改数组大小，并且迭代器无效后删除操作。从向量中删除元素效率低下，您可能想使用std :: set。

*EDIT : I removed the else section. The iterator was iterated twice *

Errors when running :

File: c:\program files (x86)\microsoft visual studio 10.0\vc\include\vector Line: 99

Expression: vector iterator not incrementable

---

File: c:\program files (x86)\microsoft visual studio 10.0\vc\include\vector Line: 100

Expression: "Standard C++ Libraries Out of Range" && 0

My code has to send alarms when it finds a new picture in a directory. But as I cannot delete the files by myself I had to trick. Before sending an alarm when I find an image, I compare it with pictures already sent(sentPictures). And in sentPictures I delete the images erased in the directory, because if I have to compare each time with every image that were found in the past, the program might be a bit heavy xD (it's in an infinite loop)

This is were I get the error. To find if the stored elements are still in the directory, I compare the old elements vector (sentPictures) with the new one (refreshVector). For every old element (sentPictures), if they are not found in the refreshVector, I delete them one by one. In my case I get the error even if nothing is done. Just walking through this loop crashes. In my case I have 9 elements in the directory, it prints 5 and crashes. I checked and there are as nuch elements in sentPictures then in refreshVector. I imagine I do not handle well the use of iterators. Here is the piece of code.

for(std::vector<Picture>::iterator it = sentPictures.begin(); it != sentPictures.end(); it++){
        std::cout << "1" << std::endl;

        if(std::find(refreshVector.begin(), refreshVector.end(), *it) == refreshVector.end()){ 
            tcout << *it <<std::endl;
            //if picture not found in refresh vector, then delete it
            //delete *it;
            //it = refreshVector.erase(it);
        }else{
            std::cout<< "2" <<std::endl;
            ++it;
        }

    }

PS : the instruction delete * it; doesn't compile. VS says "expression must have pointer or handle type", underlying "*" symbol. I'm gonna search if it isn't about the fact "it" is used in the if condition.

解决方案

The instruction delete * it; doesn't compile.

You are trying to delete an object, delete takes a pointer. You also should NEVER delete/delete[] anything was not allocated using new/new[], which seems you are not since you have a vector with objects ( not pointers).

If you want to remove sth from a container you should use its appropriate function vector<T>::erase(). delete is only for objects allocated on the heap.

Also, in case of a vector you don't have to use an iterator you can safely use an index.

for(int i=0; i != sentPictures.size(); i++)
{
   sentPictures[i]; //
   //etc
}

Though a find function will still return an iterator.

Another note, don't post-increment an iterator, it will do a redundant copy, pre-increment it instead, though am not sure if the compiler will optimize that.

Now the erase problem seems to be ruled, I need to go through this code until its end. It crashes somewhere in the lopp but don't know why.

It crashes because you're erasing inside the loop; the array size is changed when removing an element, and the iterator will be invalid after the remove operation. Removing elements from a vector is inefficient, you may want to use a std::set.

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