我正在使用二维数组形式的矩阵制作曲线拟合程序,但编译器随机抛出 BAD_ACCESS 错误,例如线程 1:EXC_BAD_ACCESS(代码= 1,地址= 0x13f800000)。该程序有时可以运行,有时会崩溃。任何想法,将不胜感激。谢谢。
- (void)main {
NSLog(@"Enter size");
scanf("%i", &matrixSize);
float* temp;
matrix = (float**)calloc(matrixSize, sizeof(float*));
temp = (float*)calloc(matrixSize+1, sizeof(float));
for (int i = 0; i < matrixSize+1; i++) {
matrix[i] = temp + (i*(matrixSize+1));
}
[self enterPoints];
[self elimination];
[self setNeedsDisplay:YES];
free(matrix);
free(temp);
}
//points entered here
- (void)enterPoints {
CGPoint *points = (CGPoint *)malloc(matrixSize * sizeof(CGPoint));
for (int i = 0; i < matrixSize; i++) {
scanf("%lf", &points[i].x);
scanf("%lf", &points[i].y);
}
for (int j = 0; j < matrixSize; j++) {
for (int i = 0; i < matrixSize+1; i++) {
if (i == (matrixSize)) {
matrix[i][j] = points[j].y;
}
else {
matrix[i][j] = pow(points[j].x, (matrixSize-1)-i);
}
}
}
free(points);
}
//matrix reduction occurs here
- (void)elimination {
for (int j = 0; j < matrixSize; j++) {
double divideValue = matrix[j][j];
for (int i = 0; i < matrixSize+1; i++) {
matrix[i][j] /= divideValue;
}
for (int j1 = 0; j1 < matrixSize; j1++) {
if (j1 == j) {
if (j1 == matrixSize-1) {
break;
}
else {
j1++;
}
}
double subValue = matrix[j][j1];
for (int i = 0; i < matrixSize+1; i++) {
matrix[i][j1] -= matrix[i][j]*subValue;
}
}
}
}
//drawing the polynomial
- (void)drawRect:(NSRect)dirtyRect {
NSGraphicsContext * GraphicsContext = [NSGraphicsContext currentContext];
CGContextRef context = (CGContextRef) [GraphicsContext graphicsPort];
CGContextSetRGBStrokeColor(context, 0.0, 0.0, 0.0, 1.0);
CGContextSetLineWidth(context, 3.0);
CGContextMoveToPoint(context, 0, matrix[matrixSize][0]*100 + 100);
[GraphicsContext saveGraphicsState];
CGMutablePathRef path;
path = CGPathCreateMutable();
for (float i = -matrixSize; i < matrixSize; i+=.01) {
float y = 0;
for (int j = 0; j < matrixSize; j++) {
y += matrix[matrixSize][j]*pow(i, j);
}
CGContextAddLineToPoint(context, i*100 + 100, y*100 + 100);
}
CGContextStrokePath(context);
[GraphicsContext restoreGraphicsState];
}
最佳答案
您没有为矩阵分配足够的内存。此行设置了整个数据区域,但您只分配了 matrixSize+1
元素,而不是 matrixSize*(matrixSize+1)
:
temp = (float*)calloc(matrixSize+1, sizeof(float));
因此,维护 matrixSize+1
列和 matrixSize
行:
matrix = (float**)calloc(matrixSize, sizeof(float*));
temp = (float*)calloc(matrixSize * (matrixSize+1), sizeof(float));
for (int i = 0; i < matrixSize; i++) {
matrix[i] = temp + (i*(matrixSize+1));
}
以后使用这个的时候要小心。您的解决方式是错误的:
for (int j = 0; j < matrixSize; j++) {
for (int i = 0; i < matrixSize+1; i++) {
if (i == (matrixSize)) {
matrix[i][j] = points[j].y;
}
else {
matrix[i][j] = pow(points[j].x, (matrixSize-1)-i);
}
}
}
请注意,i
转到 matrixSize+1
,但您将其用作行索引(只有 matrixSize
行)。我认为您打算使用matrix[j][i]
而不是matrix[i][j]
。您在构造初始矩阵时也可以这样做,但实际上我已将其更改为符合您的分配。
所以我发现你的程序中有两点缓冲区溢出。
关于objective-c - Objective-C 中的动态二维 C 数组崩溃,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13057703/