how to allocate memory for these arrays.. in mex
1 次查看(过去 30 天)
显示 更早的评论
i am trying to compile a mex file. which has variable sized arrays and i found out these arrays should be dynamically allocated.. Here i tried to allocate the arrays but still i am getting error. Can someone check my mex file and arrays. Here Z is output which is array of variable size how to accommodate this?
float *B;
B= (float *)malloc(sizeof(float)*rmax*cmax*f2);
float B[rmax*cmax][f2];
free(B);
0 个评论
采纳的回答
James Tursa
2015-5-28
编辑:James Tursa
2015-5-28
It is not entirely clear what you need help with. Are you trying to dynamically create 2D or 3D arrays of variable size? I.e., are you trying to create arrays on the fly with variable size, but still use the [ ][ ][ ] indexing syntax? If so, the answer is you can't do this directly in C (although you could easily do this in that "ancient" language called Fortran). My advice is to abandon the [ ][ ][ ] indexing syntax in your function. There is a way to do it, but you have to allocate pointer arrays off to the side to facilitate the syntax. Instead, just do the indexing manually. E.g., to create a "2D" matrix dynamically of size [A][B], one could do this:
int A = whatever;
int B = whatever;
// double x[A][B] substitute:
double *x;
x = (double *) mxMalloc( A * B * sizeof(*x) );
Then whenever you want to reference x[i][j] in your code, you would write this instead:
x[j+i*B]
Another little trick that some programmers use is to create a macro that facilitates the indexing. E.g.,
#define X(i,j) x[(j)+(i)*B]
Then whenever you would normally have written x[i][j], you can just write X(i,j) instead.
I will make another observation as well. In your text you state "... Z is output which is array of variable size ...". Are you aware that none of the X, I, and z variables in the function argument list are arrays? They are all pointers. The first level of [ ] is always interpreted as "pointer to" when used in a function argument list.
更多回答(0 个)
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Resizing and Reshaping Matrices 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!