释放对象的校验和不正确

Question

我收到此错误(内存位置因运行而异):

q2(4910,0x7fff7a1d4300) malloc: *** error for object 0x7fdf79c04bd8: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug
Abort trap: 6

这是崩溃的功能:

public:
// construct a 'rows X cols' matrix.
SMatrix(int rows, int cols) {
    if (rows<1 || cols<1) {
        cout<<"Invalid row/col value(s).";
        exit(-1);
    }
    this->_rows = rows;
    this->_cols = cols;
    this->_vertical = new simpleNode [rows];
    this->_horizontal = new simpleNode [cols];
    if (this->_vertical == NULL || this->_horizontal==NULL) {
        cout<<"Exiting";
        exit(-1);
    }
    initArrays();
}

它崩溃在这条特定的线上:

  this->_horizontal = new simpleNode [cols];

调用的函数:

int main() {
      SMatrix bigM(500,500);
      bigM.setElement(10,20,17);
      cout <<" bigM - total size in bytes: (implementation depended): "
       << bigM.sizeInBytes() << endl << endl; 

      SMatrix m1(7,10),m2(7,10),m4(10,2),m5(7,2); //Crashes on m4(10,2)
}

其他可能相关的功能:

struct simpleNode {
    Node* _next;
};
int _rows; //Number of rows in this SMatrix
int _cols; //Number of columns in this SMatrix
simpleNode * _vertical; //array (simpleNode)
simpleNode * _horizontal;  //array (simpleNode)
/*Initiate the horizontal/vertical arrays to point to null*/
void initArrays() {
    int i;
    for (i=0; i<this->_rows; i++)
        this->_horizontal[i]._next = NULL;
    for (i=0; i<this->_cols; i++)
        this->_vertical[i]._next = NULL;
}

我在OSX上.我用-g编译并用GDB运行它但程序正常退出. 如果我不使用XCode,我该如何调试？此外,如何解决问题的提示将非常有帮助.

编辑:我正在运行输出文件,有时它运行,而其他人则给我错误.似乎是随机顺序.此外,程序永远不会失败,当我在gdb上运行它总是正确退出.为什么会这样？

Answer 1

初始化代码中的限制相反.您可以像这样创建数组:

this->_vertical = new simpleNode [rows];   // <== uses rows for sizing vertical
this->_horizontal = new simpleNode [cols]; // <== uses cols for sizing horizontal

但是你的初始化是这样的:

for (i=0; i<this->_rows; i++) // <== limit is rows, but you walking horizontal
    this->_horizontal[i]._next = NULL;
for (i=0; i<this->_cols; i++) // <== limit is cols, but you walking vertical
    this->_vertical[i]._next = NULL;

除非rows和cols是相同的值,否则此代码将调用未定义的行为.通过使用与分配大小相同的值来解决此问题

for (i=0; i<this->_rows; i++)
    this->_vertical[i]._next = NULL;
for (i=0; i<this->_cols; i++)
    this->_horizontal[i]._next = NULL;

老实说,一个更好的方法会使用RAII容器std::vector<>,但我把它作为锻炼给你.

祝你好运,并希望它有所帮助.