爲什麼我的打印函數爲我的postfix程序產生這個錯誤？

Question

我想編寫一個程序來計算後綴表達式，它包括一個驅動程序和一個實現文件。這兩個如下圖所示：

#include <cstdlib> 
#include <iostream> 
#include <string> 
#include "Stack.h" 

using namespace std; 

void printStack(Stack<float>); 

int main() 
{ 
Stack<float> postFix; 
float userIn, operand1, operand2; 
// while the end of the postfix hasn't been reached 
do 
{ 
    // prompt user for next number or modulus command 
    cout << "ENTER: "; 
    if (!postFix.isEmpty()) printStack(postFix); 
    string userInput; 
    cin >> userInput; 

    // If user input is q or Q then terminate program 
    if (userInput == "q" || userInput == "Q") return 0; 
    else 
    { 
    // read next token by parsing userInput 
    // if token is a number push it onto stack 
    if (userInput != "+" && userInput != "/" && userInput != "*" && userInput != "-") 
    { 
    userIn = atof(userInput.c_str()); 
    postFix.push(userIn); 
    } 
    else if (!(postFix.size() < 2)) 
    { 
    // if it's not a number then pop element from the stack and call it 
    // operand2 
    operand2 = postFix.lastElem(); 
    postFix.pop(); 

    // pop another element from the stack; call it operand1 
    operand1 = postFix.lastElem(); 
    postFix.pop(); 

    // Perform the operation: operand1 token operand2 and 
    // push the result of the operation onto the stack 
    if (userInput == "/") 
     postFix.push((operand1/operand2)); 
    else if (userInput == "*") 
     postFix.push((operand1 * operand2)); 
    else if (userInput == "+") 
     postFix.push((operand1 + operand2)); 
    else if (userInput == "-") 
     postFix.push((operand1 - operand2)); 
    } 
    else if (postFix.size() < 2) 
    cout << "Stack is too small, request ignored\n"; 
} // end else 

} while (!postFix.isEmpty()); // end while 

// empty the stack 
postFix.makeEmpty(); 

return 0; 
} 

// The problem is in the print function! 

void printStack(Stack<float> postFix) 
{ 
    do 
    { 
    cout << postFix.lastElem() << " "; 
    postFix.pop(); 
    } while (!postFix.isEmpty()); 
} 

我實現文件如下所示：

#include <iostream> 
using namespace std; 

template <class DataType> 
class Stack 
{ 
    public: 
    Stack() // constructor 
    { 
    capacity = 2; 
    //Stack(capacity); 
    elements = new DataType[capacity]; 
    top = -1; 
    } 

    Stack(int s) // constructor with one parameter 
    { 
    capacity = s; 
    elements = new DataType[capacity]; 
    top = -1; 
    } 

~Stack() 
{ 
    delete [] elements; 
} 

bool isEmpty() const {return -1 == top;} 

void pop() // pop function 
{ 
    //if (-1 == top) return; // failed 
    top--; 
    if (top > 2 && top < (capacity/4)) 
    { 
    capacity /= 2; 
    changeSize(capacity); 
    } 
} 

DataType & lastElem() 
{ 
    return elements[top]; 
} 

int size() {return top;} 

void push(float parameter) // push function 
{ 
    if (++top == capacity) 
    { 
    capacity *= 2; 
    changeSize(capacity); 
    } 
    elements[top] = parameter; 
} 

bool peek(DataType& parameter) const 
{ 
    if (-1 == top) return false; // failed 
    parameter = elements[top]; 
    return true; // success 
} 

inline DataType & operator=(const Stack<DataType>& a) 
{ 
    if (this != &a) 
    { 
    delete [] elements; 
    elements = 0; 
    capacity = a.capacity; 
    if (capacity > 0) 
     elements = new DataType[capacity]; 
    for (int i = 0; i < capacity; i++) 
     elements[i] = a.elements[i]; 
    top = a.top; 
    } 
    return *this; 
} 

void changeSize(float newSize) // function for changing the array size if it's too small 
{ 
    DataType *newArray = new DataType[(int)newSize]; 
    int limit = (newSize > capacity)? capacity : newSize; 

    for (int i = 0; i < limit; i++) 
    { 
    newArray[i] = elements[i]; 
    } 
    delete [] elements; 
    elements = newArray; 
    capacity = newSize; 
} 

void makeEmpty() {top = -1;} 

private: 
    DataType* elements; 
    int capacity; 
    int top; // track newest value 
}; 

我編譯使用G ++這個程序後，我最多可以輸入兩個值，直到我得到如下一個奇怪的內存錯誤：

ENTER: 23 
ENTER: 23 43 
*** glibc detected *** ./calc: double free or corruption (fasttop): 0x0000000000c86010 *** 
======= Backtrace: ========= 
/lib/libc.so.6(+0x78b06)[0x7fbd11e4ab06] 
/lib/libc.so.6(cfree+0x73)[0x7fbd11e513d3] 
./calc[0x401197] 
./calc[0x400d9b] 
/lib/libc.so.6(__libc_start_main+0xfd)[0x7fbd11df0c4d] 
./calc[0x400c09] 
======= Memory map: ======== 
00400000-00402000 r-xp 00000000 08:06 788295        /home/badr/Documents/My programs/COMSC-210/calc 
00601000-00602000 r--p 00001000 08:06 788295        /home/badr/Documents/My programs/COMSC-210/calc 
00602000-00603000 rw-p 00002000 08:06 788295        /home/badr/Documents/My programs/COMSC-210/calc 
00c86000-00ca7000 rw-p 00000000 00:00 0         [heap] 
7fbd0c000000-7fbd0c021000 rw-p 00000000 00:00 0 
7fbd0c021000-7fbd10000000 ---p 00000000 00:00 0 
7fbd11dd2000-7fbd11f4f000 r-xp 00000000 08:06 5813      /lib/libc-2.11.1.so 
7fbd11f4f000-7fbd1214e000 ---p 0017d000 08:06 5813      /lib/libc-2.11.1.so 
7fbd1214e000-7fbd12152000 r--p 0017c000 08:06 5813      /lib/libc-2.11.1.so 
7fbd12152000-7fbd12153000 rw-p 00180000 08:06 5813      /lib/libc-2.11.1.so 
7fbd12153000-7fbd12158000 rw-p 00000000 00:00 0 
7fbd12158000-7fbd1216e000 r-xp 00000000 08:06 1268      /lib/libgcc_s.so.1 
7fbd1216e000-7fbd1236d000 ---p 00016000 08:06 1268      /lib/libgcc_s.so.1 
7fbd1236d000-7fbd1236e000 r--p 00015000 08:06 1268      /lib/libgcc_s.so.1 
7fbd1236e000-7fbd1236f000 rw-p 00016000 08:06 1268      /lib/libgcc_s.so.1 
7fbd1236f000-7fbd123f1000 r-xp 00000000 08:06 5814      /lib/libm-2.11.1.so 
7fbd123f1000-7fbd125f0000 ---p 00082000 08:06 5814      /lib/libm-2.11.1.so 
7fbd125f0000-7fbd125f1000 r--p 00081000 08:06 5814      /lib/libm-2.11.1.so 
7fbd125f1000-7fbd125f2000 rw-p 00082000 08:06 5814      /lib/libm-2.11.1.so 
7fbd125f2000-7fbd126e8000 r-xp 00000000 08:06 322753      /usr/lib/libstdc++.so.6.0.13 
7fbd126e8000-7fbd128e8000 ---p 000f6000 08:06 322753      /usr/lib/libstdc++.so.6.0.13 
7fbd128e8000-7fbd128ef000 r--p 000f6000 08:06 322753      /usr/lib/libstdc++.so.6.0.13 
7fbd128ef000-7fbd128f1000 rw-p 000fd000 08:06 322753      /usr/lib/libstdc++.so.6.0.13 
7fbd128f1000-7fbd12906000 rw-p 00000000 00:00 0 
7fbd12906000-7fbd12926000 r-xp 00000000 08:06 5815      /lib/ld-2.11.1.so 
7fbd12afa000-7fbd12afe000 rw-p 00000000 00:00 0 
7fbd12b21000-7fbd12b25000 rw-p 00000000 00:00 0 
7fbd12b25000-7fbd12b26000 r--p 0001f000 08:06 5815      /lib/ld-2.11.1.so 
7fbd12b26000-7fbd12b27000 rw-p 00020000 08:06 5815      /lib/ld-2.11.1.so 
7fbd12b27000-7fbd12b28000 rw-p 00000000 00:00 0 
7fff78cf3000-7fff78d08000 rw-p 00000000 00:00 0       [stack] 
7fff78dff000-7fff78e00000 r-xp 00000000 00:00 0       [vdso] 
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0     [vsyscall] 
ENTER: 43 0 Aborted 

經過多次調試我已經確定的問題必須在位於.cpp文件的打印功能：

// The problem is in the print function! 

void printStack(Stack<float> postFix) 
{ 
    do 
    { 
    cout << postFix.lastElem() << " "; 
    postFix.pop(); 
    } while (!postFix.isEmpty()); 
} 

我只是不知道爲什麼發生或如何克服它。

Answer 1

void printStack(Stack<float> postFix)以參數的值，所以做了一個副本。使用編譯器生成的拷貝構造函數。哪一個做了淺拷貝。你需要實現你自己的，做一個深層複製。

您已擁有一個複製賦值運算符（operator =）和一個析構函數。這是正確的，但還不夠。這兩個加上覆制構造函數Stack(const Stack<DataType>& other)組成了三條規則。如果你需要其中的一個，你需要全部。通常情況下，當你在班級中管理記憶時，你需要他們全部，你就是這樣。

實現類似於的operator =：

DataType(const Stack<DataType>& a) 
{ 
    elements = 0; 
    capacity = a.capacity; 
    if (capacity > 0) 
     elements = new DataType[capacity]; 
    for (int i = 0; i < capacity; i++) 
     elements[i] = a.elements[i]; 
    top = a.top; 
} 

而且，萬一這不是教育目的，有一個預執行的頭<stack>，您可以使用std::stack。