push_back不向向量C++添加数字

Question

我试图调试我的mergesort程序，这似乎是有问题的地方内的“合并”函数，当我尝试使用“push_back”从向量添加值“左”或“右”到“mergedList”。以下是gdb调试会话摘录（后面是我的完整程序代码）

这发生在第一次调用合并;我可以使用“print left [0]”访问“vector left”的值，并且我得到了一个我期待的值（向量“left”中的所有数字都在1-50000之间），但是在执行代码当我= 0：

“mergedList.push_back（left [i]）;”然后使用调试器打印mergedList [0]，看起来添加left [0]失败。

我误解了push_back？或矢量？对不起，如果我的问题不清楚 - 请让我知道我该如何改进它！

---

GDB调试会话：

---

(gdb) print left[0] 
$1 = (int &) @0x100104760: 14108 
(gdb) print mergedList[0] 
$2 = (int &) @0x7fff5fbfdbf0: 1066800 
(gdb) 
(gdb) info locals 
t = 0 
i = 0 
mergedList = { 
    <std::_Vector_base<int,std::allocator<int> >> = { 
    _M_impl = { 
     <std::allocator<int>> = { 
     <__gnu_cxx::new_allocator<int>> = {<No data fields>}, <No data fields>}, 
     members of std::_Vector_base<int,std::allocator<int> >::_Vector_impl: 
     _M_start = 0x7fff5fbfdbf0, 
     _M_finish = 0x7fff5fbfdc68, 
     _M_end_of_storage = 0x7fff5fbfdb90 
    } 
    }, <No data fields>} 
j = 0 
sizeOfLeft = 1 
sizeOfRight = 1 
next = 1 
(gdb) 
-uuu:**-F1 *gud-p1*  Bot L28 (Debugger:run)-------------------------------------- 


    ------------------------------------------------------------------------------------------------------------------ 
    while (iss >> n) 
    { 
      v.push_back(n); 
    } 

    } 

    return v; 
} 

vector<int> merge(vector<int> left, vector<int> right){ 

    int i = 0; 
    int j = 0; 
    int sizeOfLeft = left.size(); 
    int sizeOfRight = right.size(); 
    vector<int> mergedList; 

    while (i < sizeOfLeft || j < sizeOfRight){ 
    if (i < sizeOfLeft && j < sizeOfRight){ 
      if (left[i] < right[j]) { 
     mergedList.push_back(left[i]); 
=>   i++; 
      }else{ 
       mergedList.push_back(right[j]); 
     j++; 
-uu-:---F1 main.cpp  21% L47 (C++/l Abbrev)-------------------------------------------------------------------------------------------------------------------------------------------------------- 


    #COMPLETE MERGESORT PROGRAM 



    #include <iostream> 
    #include <fstream> 
    #include <sstream> 
    #include <string> 
    #include <vector> 

    using namespace std; 

vector<int> getNums(){ 


    ifstream infile("/Users/christinedeist/Documents/Algorithms/Practice/TestProject/IntegerArray.txt"); 
    string line; 
    vector<int> v; 

    while (getline(infile, line)) 
    { 
     istringstream iss(line); 
     int n; 

     while (iss >> n) 
     { 
      v.push_back(n); 
     } 

    } 

    return v; 
} 

vector<int> merge(vector<int> left, vector<int> right){ 

    int i = 0; 
    int j = 0; 
    int sizeOfLeft = left.size(); 
    int sizeOfRight = right.size(); 
    vector<int> mergedList; 

    while (i < sizeOfLeft || j < sizeOfRight){ 
     if (i < sizeOfLeft && j < sizeOfRight){ 
      if (left[i] < right[j]) { 
       mergedList.push_back(left[i]); 
       i++; 
      }else{ 
       mergedList.push_back(right[j]); 
       j++; 
      } 

     }else if (i < sizeOfLeft){ 
      mergedList.push_back(left[i]); 
      i++; 
     }else if (j < sizeOfRight){ 
      mergedList.push_back(right[j]); 
      j++; 
     } 
    } 


    return mergedList; 

} 

vector<int> sortVector(vector<int> nums){ 

    int sizeOfNums = nums.size(); 

    if (sizeOfNums == 1){ 
     return nums; 
    } 
    vector<int> left; 
    vector<int> right; 
    int midpoint = sizeOfNums/2; 
    for (int i = 0; i < midpoint; i++){ 
     left.push_back(nums[i]); 

    } 
    for (int j = midpoint; j < sizeOfNums; j++){ 
     right.push_back(nums[j]); 
    } 
    left = sortVector(left); 
    right = sortVector(right); 
    return merge(left, right); 

} 

int main (int argc, char *argv[]) { 

    vector<int> nums = getNums(); 
    vector<int> sorted = sortVector(nums); 

    for(int i = 0; i < nums.size(); i++){ 
     cout << nums[i] <<endl; 

    } 

    return 0; 
} 

Answer 1

此代码缺少错误检查，但应该仍然可以工作。我认为这个逻辑应该可以正常工作。您是否尝试调试此代码，因为它没有生成已排序的输出。最后，当您对元素进行排序时，您不会打印排序元素，而是显示您阅读的元素。

因为您的gdb会话在向量中有指针的非空值，即_M_start = 0x7fff5fbfdbf0, _M_finish = 0x7fff5fbfdc68, _M_end_of_storage = 0x7fff5fbfdb90这有一些元素被推入向量中。因此，文件必须打开并成功读取。