<BadPtr>迴路上的錯誤

Question

每當我到達代碼中的這一點時，我都會收到一個BadPtr錯誤：爲什麼？

for(int i = 0; i < processTable.size(); i++) 
     { 
      data_entry test = *processTable.at(i).dataCurrent; //ERROR 
      cout << test.text << "\n"; 
     } 

這裏是我的代碼：

#include "stdafx.h" 
#include <iostream> 
#include <string> 
#include <fstream> 
#include <vector> 

using namespace std; 

enum process_state { READY, RUNNING, WAITING }; 

struct data_entry { 
    const char * text; 
    int time; 
}; 

struct process_entry 
{ 
    int process; 
    const data_entry * dataStart; 
    const data_entry * dataEnd; 
    const data_entry * dataCurrent; 
    process_state state; 
}; 

int _tmain(int argc, _TCHAR* argv[]) 
{ 
    vector<data_entry> dataTable; 
    vector<process_entry> processTable; 

    string line; 
    ifstream myfile ("C:\\Users\\1162852\\Documents\\visual studio 2010\\Projects\\Project 1 (OS)\\Debug\\input.txt"); 
    if (myfile.is_open()) 
    { 
     int processAmount = 0; 

     while (getline (myfile,line)) 
     { 
      if(line.find("START") != string::npos) 
      { 
       data_entry newEntry; 
       newEntry.text = "START"; 
       newEntry.time = atoi(line.substr(6, 6).c_str()); 
       dataTable.push_back(newEntry); 

       process_entry newProcessEntry; 
       newProcessEntry.dataStart = &dataTable.at(dataTable.size() - 1); 
       newProcessEntry.dataCurrent = &dataTable.at(dataTable.size() - 1); 
       newProcessEntry.process = processAmount; 
       processTable.push_back(newProcessEntry); 

       processAmount += 1; 
      } 
      else if(line.find("END") != string::npos) 
      { 
       data_entry newEntry; 
       newEntry.text = "END"; 
       newEntry.time = NULL; 
       dataTable.push_back(newEntry); 

       processTable.at(processTable.size() - 1).dataEnd = &dataTable.at(dataTable.size() - 1); 
      } 
      else if(line.find("RUN") != string::npos) 
      { 
       data_entry newEntry; 
       newEntry.text = "RUN"; 
       newEntry.time = atoi(line.substr(4, 4).c_str()); 
       dataTable.push_back(newEntry); 
      } 
      else if(line.find("INPUT") != string::npos) 
      { 
       data_entry newEntry; 
       newEntry.text = "INPUT"; 
       newEntry.time = atoi(line.substr(6, 6).c_str()); 
       dataTable.push_back(newEntry); 
      } 
      else if(line.find("SSD") != string::npos) 
      { 
       data_entry newEntry; 
       newEntry.text = "SSD"; 
       newEntry.time = atoi(line.substr(4, 4).c_str()); 
       dataTable.push_back(newEntry); 
      } 
     } 

     //reverse(dataTable.begin(),dataTable.end()); 
     /*for(int i = 0; i < dataTable.size(); i++) 
     { 
      cout << dataTable.at(i).text << "\n"; 
     }*/ 

     for(int i = 0; i < processTable.size(); i++) 
     { 
      data_entry test = *processTable.at(i).dataCurrent; 
      cout << test.text << "\n"; 
     } 
     myfile.close(); 
    } 

    int test; 
    cin >> test; 
    return 0; 
} 

Answer 1

問題是，你正在保存一個指向元素dataTable的指針，但是如果矢量調整大小，則push_back會使這些指針無效。考慮將dataTable和processTable作爲共享指針的向量，以免它們移動。

vector<shared_ptr<data_entry>> dataTable; 
vector<shared_ptr<process_entry>> processTable; 

我還會將process_entry的成員更改爲共享指針，而您在此處。有了這些改變你的開頭部分現在是這個樣子：

  auto newEntry = make_shared<data_entry>(); 
      newEntry->text = "START"; 
      newEntry->time = atoi(line.substr(6, 6).c_str()); 
      dataTable.push_back(newEntry); 

      auto newProcessEntry = make_shared<process_entry>(); 
      newProcessEntry->dataStart = dataTable.back(); 
      newProcessEntry->dataCurrent = dataTable.back(); 
      newProcessEntry->process = processAmount; 
      processTable.push_back(newProcessEntry); 

你有另一種選擇是使用std::list當它生長，不會複製周圍的元素。

Answer 2

這種分配應該返回一個數據條目類型。 使用->dataCurrent獲取指向data_entry的指針，然後解除引用。 您可能也想將data_entry指定爲const，具體取決於它的用途。

const data_entry test = *(processTable.at(i)->dataCurrent); 

Answer 3

更換

*processTable.at(i).dataCurrent; 

通過

*(processTable.at(i).dataCurrent); 

而且你沒有拷貝構造函數，因此一個淺拷貝。 確保這是你想要的。

Answer 4

您使用在while循環內創建的局部變量填充了vectors，並且它們不能在封閉的if塊之外訪問。

所以一旦我們退出while塊，所有的局部變量都被銷燬了，vector指向了一堆bad_ptr s。