Question

我在运行Valgrind尝试递增用于模板堆栈的数组（初始大小为10）时遇到4个错误，当我尝试向数组中添加第11个元素时（恰好是当我将valgrind赋给我4个错误）必须在推送过程中增加尺寸）：

class stack {

private:
    int _size = 10;
    T *_data;
    int _top;
    int _count = 0;

public:

// costructor used
   stack(int s) {
       this->_size = s;
       _data = new T[_size];
       this->_top = -1;

   }

   ....

   void push(T v) {
        if (_count <= _size) {

        this->_top++;
        this->_data[_top] = v;  
        this->_count++;
       }else{
        //HEAP ERRORS HERE ++++++++
        _size++;
        T *temp = new T[_size];
         for(int i = 0; i < _top; i++) {
            temp[i] = _data[i];
        }
        delete [] _data;
        _data=temp;
        _data[_top] = v;        
        this->_top++;
        this->_count++;         
    }

我不确定在else语句后是否有新运算符和delete []，我认为我在那里遇到了问题，但是我想不出另一种方法来解决它。

在main.cpp中，我仅压入模板堆栈中的11个元素：

stack<int> s;
s.push(1);
s.push(2);
s.push(3);
s.push(4);
s.push(5);
s.push(6);
s.push(7);
s.push(8);
s.push(9);
s.push(10);
s.push(11);

这是valgrind的输出

 ==4178== Invalid write of size 4
 ==4178==    at 0x10921E: stack<int>::push(int) (stack.h:85)
 ==4178==    by 0x108ED2: main (main.cpp:32)
 ==4178==  Address 0x5b82ca8 is 0 bytes after a block of size 
 40 alloc'd
 ==4178==    at 0x4C3089F: operator new[](unsigned long) (in 
 /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
 ==4178==    by 0x109144: stack<int>::stack() (stack.h:28)
 ==4178==    by 0x108B8D: main (main.cpp:9)
  HEAP SUMMARY:
 ==4178==     in use at exit: 0 bytes in 0 blocks
 ==4178==   total heap usage: 4 allocs, 4 frees, 73,808 bytes 
 allocated
 ==4178== 
 ==4178== All heap blocks were freed -- no leaks are possible
 ==4178== 
 ==4178== For counts of detected and suppressed errors, rerun with: -v
 ==4178== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 
 0)

谢谢。

Answer 1

如Dave S所述，if (_count <= _size)条件导致堆损坏。将条件更改为if (_count < _size)将导致您期望的行为。

照原样，您将从0迭代到10，以进行总共11次推送，然后触发溢出。

Answer 2

您说过11次按下会导致错误。看来原因是<=。当count等于size时，您应该扩展数组，但是您的代码会将项目推到end元素之后。

请注意，常见情况是范围边缘上的错误。为了避免这种情况，请使用单元测试。还要尝试避免开发已经完成的事情，只需使用现有的一项即可。

大小为4且数组递增大小的读取无效

2 个答案: