Question

我在C ++工作。我正在研究一种改变堆栈最大容量的方法，而且我对我得到的错误感到困惑。以下是我的方法。

void Stack::setCapacity(unsigned newCapacity){
if(newCapacity< this->getSize()){
    throw StackException("setCapacity()", 
    "the size is larger than the desired capacity");
} else {
    if(newCapacity != myCapacity){
        Item * tempArray = new Item[newCapacity];
        if(newCapacity < myCapacity){
            for(unsigned i=0; i<newCapacity;i++){
                tempArray[i] = myArray[i];
            }
        } else if (newCapacity > myCapacity) {
            for(unsigned i=0; i<myCapacity; i++){
                tempArray[i] = myArray[i];
            }
        }
        for(unsigned i=0; i<newCapacity; i++){
            myArray[i] = tempArray[i];
        }
        delete tempArray;
    }
    myCapacity = newCapacity;
} 
}

我还编写了一个测试方法来测试我的setCapacity（）方法是否有效。

void StackTester::setCapacityTest() {
cout << "- setCapacity... " << flush;

// empty stack
Stack st7(5);
assert(st7.getSize() == 0);
assert(st7.getCapacity() == 5);
st7.setCapacity(7);
assert(st7.getCapacity() == 7);
cout << " 1 " << flush;

// partially filled stack - larger capacity
Stack st8(5);
assert(st8.getCapacity() == 5);
st8.push(3);
st8.push(4);
st8.setCapacity(7);
assert(st8.getCapacity() == 7);
assert(st8.getTop() == 4);
st8.pop();
assert(st8.getTop() == 3);
cout << " 2 " << flush;

// size larger than new capacity
try{
Stack st9(3);
st9.push(7);
st9.push(4);
st9.push(11);
assert(st9.getSize() == 3);
st9.setCapacity(2);
cerr << "setCapacity's new capacity is larger than the size";
exit(1);
} catch(StackException& se){
    cout << " 3 " << flush;
}

// partially filled stack - smaller capacity
Stack st10(5);
assert(st10.getCapacity() == 5);
st10.push(1);
st10.setCapacity(2);
assert(st10.getCapacity() == 2);
assert(st10.getTop() == 1);
cout << " 4 " << flush;

// fully filled stack - larger capacity
Stack st11(2);
assert(st11.getCapacity() == 2);
st11.push(3);
st11.push(7);
assert(st11.getTop() == 7);
st11.setCapacity(3);
assert(st11.getCapacity() == 3);
cout << " 5 " << flush;

cout << " Passed!" << endl;
}

当我通过评论其余部分单独运行测试的每个部分时，一切正常。测试的每个部分都通过了。但是，当我组合这些部分并尝试运行整个测试时，我收到以下错误：

*检测到glibc ** * / home /.../StackProject：malloc（）：内存损坏（快速）：0x0000000001e86030 *

使用调试器，我已经将问题缩小到在堆栈中创建myArray。例如，成功运行＆＃34; 1＆＃34;在我的测试中，在＆＃34;中的st8（5）中创建了myArray。 2＆＃34;导致程序崩溃。

我混淆的主要原因是每个部分单独通过，但它们没有集体通过。我不知道该怎么做。我的方法写错了吗？如果是这样，我该如何纠正呢？

谢谢。

Answer 1

你有

delete tempArray;

但它是一个数组，所以你必须这样做：

delete [] tempArray;

（虽然我不知道这个功能在做什么或为什么......）

Answer 2

我在setCapacity中看到以下问题，在以下代码块中：

  if(newCapacity != myCapacity){
     Item * tempArray = new Item[newCapacity];
     if(newCapacity < myCapacity){
        for(unsigned i=0; i<newCapacity;i++){
           tempArray[i] = myArray[i];
        }
     } else if (newCapacity > myCapacity) {
        for(unsigned i=0; i<myCapacity; i++){
           tempArray[i] = myArray[i];
        }
     }

     // When newCapacity > myCapacity, myArray does not
     // have enough space for this loop.
     // Say myCapacity = 5 and newCapacity = 7
     // Accessing myArray[5] and myArray[6] is a problem.

     for(unsigned i=0; i<newCapacity; i++){
        myArray[i] = tempArray[i];
     }

     // You are deleting the newly allocated array, even though you are using
     // the wrong delete operator.
     // myArray still points to the old allocated memory.
     delete tempArray;
  }

您需要的是：

  if(newCapacity != myCapacity){
     Item * tempArray = new Item[newCapacity];
     if(newCapacity < myCapacity){
        for(unsigned i=0; i<newCapacity;i++){
           tempArray[i] = myArray[i];
        }
     } else if (newCapacity > myCapacity) {
        for(unsigned i=0; i<myCapacity; i++){
           tempArray[i] = myArray[i];
        }
     }

     // Need to delete the old array and keep the new array.

     Item* oldArray = myArray;
     myArray = tempArray;

     // Use the array delete operator, not the simple delete operator.
     delete [] oldArray;
  }

malloc（）：内存损坏（快速）错误C ++

2 个答案: