分割错误（Malloc？）

Question

我正在使用Jacobi迭代的程序（http://en.wikipedia.org/wiki/Jacobi_iteration）。但我得到一个seg故障。该代码看起来对我来说是正确的，在这一点上我彻底沮丧。也许有人可以指出我的错误。

int main(void) { 
double* coeff_Matrix; 
int nx, ny; 

do{ 
    //Get values of nx and ny from user. 
    printf("Please enter the number of x-points and the number of y-points desired. \n"); 
    printf("\n"); 

    printf("How many x-points do you want? Enter zero for default (1024). \n"); 
    scanf("%d", &nx); 

    printf("How many y-points do you want? Enter zero for default (1024). \n"); 
    scanf("%d", &ny); 

    coeff_Matrix = NULL; 
    coeff_Matrix = (double**) malloc(nx*sizeof(double*)); //SEGMENTATION FAULT DUE TO THIS? 
    if(nx > 0) { 
     PDE_calculate(nx, ny, &coeff_Matrix); //This method is used to generate a diagonally dominant matrix. 
     jacobi_Calculate(&coeff_Matrix, nx); //This method does the Jacobi iteration. 
    } 
    else { 
     puts("Invalid choice or memory available was exceeded ... Try again."); 
      if(coeff_Matrix != NULL) 
      free(coeff_Matrix); 
    } 
}while(more()); //The more() method just asks the user if they would like to do a different problem. User just says "y/n". Mainly here to allow for expanded functionality. 

return 0; 

} //结束主

所以，你可以看到，该程序要求的x点和y点。 （容差已经通过#define语句设置）任何想法？

Answer 1

coeff_Matrix = (double**) malloc(nx*sizeof(double*)); 

你不需要键入从malloc转换返回的指针。明确地键入转换并不被认为是一种好的做法。如果您使用类型转换，它应该是double *。但它不是明确键入强制转换的好习惯。所以最好将malloc的输出分配给一个指针。类型转换将被隐式处理。

Answer 2

看来你已经混淆了指针的整个想法。

为了动态声明大小的多维数组（M，N），这样做：

int **array; 
int m=4,n=3,i; 

array=malloc(sizeof(int *)*m); 
for (i=0;i<m;i++) 
    array[i]=malloc(sizeof(int)*n); 

所以，因为这会改变你的程序：

int main(void) { 
double** coeff_Matrix; 
int nx, ny, i; 

do{ 
    //Get values of nx and ny from user. 
    printf("Please enter the number of x-points and the number of y-points desired. \n"); 
    printf("\n"); 

    printf("How many x-points do you want? Enter zero for default (1024). \n"); 
    scanf("%d", &nx); 

    printf("How many y-points do you want? Enter zero for default (1024). \n"); 
    scanf("%d", &ny); 

    coeff_Matrix = NULL; 
    coeff_Matrix = (double**) malloc(nx*sizeof(double*)); // you don't need to cast the result of malloc though 

    for (i=0;i<nx;i++) 
     coeff_Matrix[i]=(double *)malloc(ny*sizeof(double)); 

    if(nx > 0) { 
     PDE_calculate(nx, ny, coeff_Matrix); //This method is used to generate a diagonally dominant matrix. 
     jacobi_Calculate(coeff_Matrix, nx); //This method does the Jacobi iteration. 
    } 
    else { 
     puts("Invalid choice or memory available was exceeded ... Try again."); 
      if(coeff_Matrix != NULL) 
      { 
       for (i=0;i<nx;i++) 
        free(coeff_Matrix[i]); 

       free(coeff_Matrix); 
      } 
    } 
}while(more()); //The more() method just asks the user if they would like to do a different problem. User just says "y/n". Mainly here to allow for expanded functionality. 

return 0; 
}