Question

我正在为数学项目编写一个矩阵类，我有一个奇怪的问题，即我写的复制构造函数在一个函数中失败但在另一个函数中成功 - 并且情况看似相同。我通过gdb运行它并且复制构造函数执行但不知何故只是在它完成后没有分配值。

以下是gdb的输出：

(gdb) break main.cpp:20
Breakpoint 1 at 0x8048913: file main.cpp, line 20.
(gdb) run
Starting program: /home/ian/Documents/math471/src/compress 
printing
1 1 1 1 
1 2 3 4 
1 3 5 7 
1 4 7 10 
printing
1 1 1 1 
1 2 3 4 
1 3 5 7 
1 4 7 10 
printing
1 1 1 1 
1 2 3 4 
1 3 5 7 
1 4 7 10 
printing
1 1 1 1 
1 2 3 4 
1 3 5 7 
1 4 7 10 

Breakpoint 1, main (argc=1, argv=0xbffff334) at main.cpp:20
20          tridiagonalize(A);
(gdb) s
tridiagonalize (A=...) at tridiagonalize.cpp:10
10          Matrix result(A);
(gdb) print result
$1 = {transposed = false, height = 3903476, width = 0, data = 0x0}
(gdb) s
Matrix::Matrix (this=0xbffff23c, A=...) at matrix.cpp:176
176         height = A.getHeight();
(gdb) print height
$2 = 0
(gdb) n
177         width = A.getWidth();
(gdb) print height
$3 = 4
(gdb) n
178         data = new double*[height];
(gdb) print width
$4 = 4
(gdb) n
179         for(int i = 0; i < height; i++){
(gdb) break matrix.cpp:185
Breakpoint 2 at 0x80492ba: file matrix.cpp, line 185.
(gdb) c
Continuing.

Breakpoint 2, Matrix::Matrix (this=0xbffff23c, A=...) at matrix.cpp:185
185         transposed = false;
(gdb) n
186 }
(gdb) print transposed
$5 = false
(gdb) print this
$6 = (Matrix * const) 0xbffff23c
(gdb) print this->height
$7 = 4
(gdb) n
tridiagonalize (A=...) at tridiagonalize.cpp:11
11          int n = A.getWidth();
(gdb) print result
$8 = {transposed = false, height = 3903476, width = 0, data = 0x0}
(gdb)

如您所见，结果中的值与构造函数之前的值相同。

#include "matrix.h"
#include "tridiagonalize.h"


using namespace std;

void function(Matrix &A);

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

        Matrix A(4, 4);
        for(int i = 0; i < 16; i++){
                A.set(i/4, i%4, (i%4)*(i/4)+1);
        }
        function(A);
        Matrix B = A;
        A.print();
        B.print();

        tridiagonalize(A);
        //A.print();

        return 0;
}

void function(Matrix &A){
        Matrix result(A);
        A.print();
        result.print();
}

Matrix tridiagonalize(Matrix &A){

        Matrix result(A);
        int n = A.getWidth();
        cout << "width: " << n << endl;
        cout << "width of result: " << result.getWidth() << endl;
            return result;
}

编辑：这是矩阵代码：

void Matrix::set(int i, int j, double value){
        if(transposed){
                int tmp = i;
                i = j;
                j = tmp;
        }
        if(i < 0 || j < 0 || i >= height || j >= width){
                cout << "trying to set value outside of matrix" << endl;
                return;
        }
        if(height > 0 && width > 0){
                data[i][j] = value;
        }
        return;
}

void Matrix::print() const{
        cout << "printing" << endl;
        if(!transposed){
                for(int i = 0; i < height; i++){
                        for(int j = 0; j < width; j++){
                                cout << data[i][j] << " ";
                        }
                        cout << endl;
                }
        }
        else{
                for(int i = 0; i < width; i++){
                        for(int j = 0; j < height; j++){
                                cout << data[j][i] << " ";
                        }
                        cout << endl;
                }
        }
        return;
}

Matrix::~Matrix(){
        //cout << "deleting Matrix" << endl;
        if(data != NULL){
                for(int i = 0; i < height; i++){
                        //cout << data[i] << endl;
                        delete[] data[i];
                }
                //cout << data << endl;
                delete[] data;
        }
}

double Matrix::get(int i, int j) const {
        if(transposed){
                int tmp = i;
                i = j;
                j = tmp;
        }
        if(data != NULL && i >=0 && j >= 0 && i < height && j < width){
                return data[i][j];
        }
        else{
                cout << "error in get" << endl;
        }
        return -1;
}

int Matrix::getHeight() const {
        if(transposed){
                return width;
        }
        else{
                return height;
        }
}

int Matrix::getWidth() const {
        if(transposed){
                return height;
        }
        else{
                return width;
        }
}



Matrix::Matrix(const Matrix& A){
        height = A.getHeight();
        width = A.getWidth();
        data = new double*[height];
        for(int i = 0; i < height; i++){
                data[i] = new double[width];
                for(int j = 0; j < width; j++){
                        data[i][j] = A.get(i,j);
                }
        }
        transposed = false;
}

Matrix Matrix::operator= (Matrix &B){
        if(data != NULL){
                for(int i = 0; i < height; i++){
                        delete[] data[i];
                }
                delete[] data;
        }
        data = NULL;
        Matrix result(B);
        return result;
}

tridiagonalize功能和＆＃39;功能＆＃39;函数设置相同，但function（）起作用，而tridiagonalize（）不起作用。任何想法为什么会发生这种情况？

编辑：添加矩阵代码

Answer 1

Matrix::operator=()无法正常工作，它会释放旧的data数组，但不会创建一个包含应该分配的数据的新数组。

它应该看起来像这样：

Matrix& Matrix::operator= (const Matrix &B){
   // Don't do anything if B is the same object
   if (&B == this)
      return *this;

   // delete data, as in the current version
   if(data != NULL){
      ...
   }

   // Create new array of arrays, fill with numbers from B
   data = new double*[B.getHeight()];
   ...

   return *this;
}

复制构造函数失败并在相同的情况下成功

1 个答案: