# 复制构造函数失败并在相同的情况下成功Copy constructor fails and succeeds in identical circumstances

``````(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)
``````

``````#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;
}
``````

``````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函数和'function'函数设置相同，但function（）工作，tridiagonalize（）不工作。 任何想法为什么会这样？

## 1 个回复1

### ===============>>#1 票数：2 已采纳

`Matrix::operator=()`无法正常工作，它释放旧`data`数组，但不会创建一个带有应分配数据的新数据。

``````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;
}
``````

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