我正在尝试制作一个可以计算闭合多边形链面积的程序。该程序似乎输出正确的结果，直到...它达到返回0;在主要功能。
调试器显示退出main函数时，程序在polygon.h中的第17行调用Vertex的析构函数，那就是当一切都变成混乱时！析构函数尝试释放Vertex *顶点指向的动态分配空间。但它没有这样做，而是给出了一个很长的错误信息，我已经粘贴在下面。
在试图解决这个问题一段时间后，我别无选择，只能寻求帮助。有人可以告诉我的程序有什么问题吗？
提前致谢
错误消息
==9715== Conditional jump or move depends on uninitialised value(s)
==9715== at 0x400C8A: Polygon::add(Vertex const&) (Polygon.cpp:25)
==9715== by 0x40147C: main (main.cpp:16)
==9715==
==9715== Invalid write of size 8
==9715== at 0x401198: Vertex::setX(int) (Vertex.h:12)
==9715== by 0x400E07: Polygon::add(Vertex const&) (Polygon.cpp:42)
==9715== by 0x40147C: main (main.cpp:16)
==9715== Address 0x5959080 is 0 bytes after a block of size 64 alloc'd
==9715== at 0x4C28147: operator new[](unsigned long) (vg_replace_malloc.c:348)
==9715== by 0x400B5E: Polygon::Polygon(Vertex*, int) (Polygon.cpp:13)
==9715== by 0x401281: main (main.cpp:8)
==9715==
==9715== Invalid write of size 8
==9715== at 0x4011B2: Vertex::setY(int) (Vertex.h:13)
==9715== by 0x400E2B: Polygon::add(Vertex const&) (Polygon.cpp:43)
==9715== by 0x40147C: main (main.cpp:16)
==9715== Address 0x5959088 is 8 bytes after a block of size 64 alloc'd
==9715== at 0x4C28147: operator new[](unsigned long) (vg_replace_malloc.c:348)
==9715== by 0x400B5E: Polygon::Polygon(Vertex*, int) (Polygon.cpp:13)
==9715== by 0x401281: main (main.cpp:8)
==9715==
num: 5
==9715== Invalid read of size 8
==9715== at 0x401174: Vertex::getY() const (Vertex.h:11)
==9715== by 0x400ED1: Polygon::area() const (Polygon.cpp:58)
==9715== by 0x4014C2: main (main.cpp:18)
==9715== Address 0x5959088 is 8 bytes after a block of size 64 alloc'd
==9715== at 0x4C28147: operator new[](unsigned long) (vg_replace_malloc.c:348)
==9715== by 0x400B5E: Polygon::Polygon(Vertex*, int) (Polygon.cpp:13)
==9715== by 0x401281: main (main.cpp:8)
==9715==
==9715== Invalid read of size 8
==9715== at 0x40115A: Vertex::getX() const (Vertex.h:10)
==9715== by 0x400F08: Polygon::area() const (Polygon.cpp:59)
==9715== by 0x4014C2: main (main.cpp:18)
==9715== Address 0x5959080 is 0 bytes after a block of size 64 alloc'd
==9715== at 0x4C28147: operator new[](unsigned long) (vg_replace_malloc.c:348)
==9715== by 0x400B5E: Polygon::Polygon(Vertex*, int) (Polygon.cpp:13)
==9715== by 0x401281: main (main.cpp:8)
==9715==
==9715== Invalid read of size 8
==9715== at 0x40115A: Vertex::getX() const (Vertex.h:10)
==9715== by 0x400F90: Polygon::area() const (Polygon.cpp:63)
==9715== by 0x4014C2: main (main.cpp:18)
==9715== Address 0x5959080 is 0 bytes after a block of size 64 alloc'd
==9715== at 0x4C28147: operator new[](unsigned long) (vg_replace_malloc.c:348)
==9715== by 0x400B5E: Polygon::Polygon(Vertex*, int) (Polygon.cpp:13)
==9715== by 0x401281: main (main.cpp:8)
==9715==
==9715== Invalid read of size 8
==9715== at 0x401174: Vertex::getY() const (Vertex.h:11)
==9715== by 0x400FED: Polygon::area() const (Polygon.cpp:64)
==9715== by 0x4014C2: main (main.cpp:18)
==9715== Address 0x5959088 is 8 bytes after a block of size 64 alloc'd
==9715== at 0x4C28147: operator new[](unsigned long) (vg_replace_malloc.c:348)
==9715== by 0x400B5E: Polygon::Polygon(Vertex*, int) (Polygon.cpp:13)
==9715== by 0x401281: main (main.cpp:8)
==9715==
area: 39
minx: -1
trianglearea: 4.5
==9715==
==9715== HEAP SUMMARY:
==9715== in use at exit: 0 bytes in 0 blocks
==9715== total heap usage: 4 allocs, 4 frees, 176 bytes allocated
==9715==
==9715== All heap blocks were freed -- no leaks are possible
==9715==
==9715== For counts of detected and suppressed errors, rerun with: -v
==9715== Use --track-origins=yes to see where uninitialised values come from
==9715== ERROR SUMMARY: 7 errors from 7 contexts (suppressed: 4 from 4)
/ * main.cpp * /
#include <iostream>
#include "Polygon.h"
using namespace std;
int main() {
Vertex varr[] = { Vertex(0,0), Vertex(6,0),
Vertex(6,6), Vertex(0,6) };
Polygon pol( varr, 4 );
cout << "num: " << pol.numVertices() << endl;
cout << "area: " << pol.area() << endl;
cout << "minx: " << pol.minX() << endl;
cout << "maxx: " << pol.maxX() << endl;
cout << "miny: " << pol.minY() << endl;
cout << "maxy: " << pol.maxY() << endl;
pol.add( Vertex(-1,3) );
cout << "num: " << pol.numVertices() << endl;
cout << "area: " << pol.area() << endl;
cout << "minx: " << pol.minX() << endl;
Polygon pol1;
pol1.add( Vertex(0,0) );
pol1.add( Vertex(3,3) );
pol1.add( Vertex(3,0) );
cout << "trianglearea: " << pol1.area() << endl;
return 0;
}
/ * Vertex.cpp * /
#include "Vertex.h"
Vertex::Vertex(int newx, int newy) {
x = newx;
y = newy;
}
/ * Vertex.h * /
#ifndef VERTEX_H
#define VERTEX_H
class Vertex {
private:
double x, y;
public:
Vertex() {x = 0; y = 0;};
Vertex(int newx, int newy);
double getX() const { return x; }
double getY() const { return y; }
void setX(const int newx) { x = newx; }
void setY(const int newy) { y = newy; }
};
/ * Polygon.cpp * /
#include "Polygon.h"
#include <cmath> // For abs
// Constructor sets array of v to be the vertices of polygon
Polygon::Polygon( Vertex * const v, const int newSize ) : size(newSize) {
// Set first element to min and max
minx = maxx = (v[0]).getX();
miny = maxy = (v[0]).getY();
// Add vertices and set min/max
int x, y;
vertices = new Vertex[size];
for (int i = 0; i < size; i++) {
x = v[i].getX();
y = v[i].getY();
(vertices[i]).setX(x);
(vertices[i]).setY(y);
if (i > 0)
setMinMax(x, y);
}
}
/* Add a single vertex */
void Polygon::add( const Vertex& v ) {
if (size == maxSize) {
maxSize *= 2;
Vertex * tempPointer = new Vertex[maxSize];
// Copy elements of previous vertice array to new one
for (int i = 0; i < size; i++) {
(tempPointer[i]).setX((vertices[i]).getX());
(tempPointer[i]).setY((vertices[i]).getY());
}
delete [] vertices;
vertices = tempPointer;
tempPointer = 0;
}
// Add single vertex to the end of vertices array
int x = v.getX();
int y = v.getY();
(vertices[size]).setX(x);
(vertices[size]).setY(y);
setMinMax(x, y);
size++;
}
/* Calculate area using formula on http://mathworld.wolfram.com/PolygonArea.html */
double Polygon::area() const {
double area = 0, term1, term2;
// Area must be 0 if nbr of vertices is < 3
if (size < 3) {
return area;
}
// Sum initial terms in formula
int i;
for (i = 0; i < size-1; i++) {
term1 = ( vertices[i].getX() * vertices[i+1].getY() ) / 2;
term2 = ( vertices[i+1].getX() * vertices[i].getY() ) / 2;
area += (term1 - term2);
}
// Sum last term in formula
term1 = (vertices[i].getX() * vertices[0].getY()) / 2;
term2 = (vertices[0].getX() * vertices[i].getY()) / 2;
area += (term1 - term2);
return fabs(area);
}
void Polygon::setMinMax(const int x, const int y) {
if (size == 0) {
minx = maxx = x;
miny = maxy = y;
}
else {
if (x < minx) { minx = x; }
if (x > maxx) { maxx = x; }
if (y < miny) { miny = y; }
if (y > maxy) { maxy = y; }
}
}
#endif /* VERTEX_H */
/ * Polygon.h * /
#ifndef POLYGON_H
#define POLYGON_H
#include "Vertex.h"
class Polygon {
private:
int size, maxSize;
Vertex * vertices;
double minx, miny, maxx, maxy;
void setMinMax(const int x, const int y);
public:
Polygon() : size(0), maxSize(1), vertices(new Vertex[1]) {}
Polygon( Vertex * const v, const int newSize );
~Polygon() { delete [] vertices; }
void add( const Vertex& v );
double area() const;
double minX() const { return minx; }
double minY() const { return miny; }
double maxX() const { return maxx; }
double maxY() const { return maxy; }
int numVertices() const { return size; }
};
#endif /* POLYGON_H */
答案 0 :(得分：5)
错误源于在构建带有数组的maxSize类期间未初始化Polygon：
Polygon::Polygon( Vertex * const v, const int newSize ) :
size(newSize), maxSize(newSize)
您应该解决代码中的其他问题。