mex內存分配mxRealloc

Question

我必須讀取一個double的矩陣，處理它的值並將它們插入一個新的矩陣，它的一個維度在開始時是未知的。

在靜態內存分配，我的代碼是：

#include <mex.h> 

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) 
{ 
    const mxArray *I = prhs[0]; 
    double *indata = mxGetPr(I); 
    double *submtx = mxGetPr(prhs[1]); 
    const int *size = mxGetDimensions(I); 
    int xp = (int)submtx[0], yp = (int)submtx[1], zp = (int)submtx[2]; 
    int xi = size[0], yi = size[1], zi = size[2]; 

    int numsubmtx = (xi - xp + 1)*(yi - yp + 1)*(zi - zp + 1); 
    int out_rows = xp*yp*zp; 
    int out_cols = numsubmtx; 
    mxArray *out = mxCreateDoubleMatrix(out_rows, out_cols, mxREAL); 
    double *outdata = mxGetPr(out); 

    int submtx_counter = 0; 
    for(int z_offset = 0; ...; z_offset++){ 
     for(int y_offset = 0; ...; y_offset++){ 
       for(int x_offset = 0; ...; x_offset++){ 
        int row = 0; 
        for(int z_counter = 0; ...; z_counter++){ 
          for(int y_counter = 0; ...; y_counter++){ 
           for(int x_counter = 0; ...; x_counter++){ 
             outdata[submtx_counter*out_rows + row] = 
              indata[ (x_offset+x_counter) + (y_offset+y_counter)*xi + (z_offset+z_counter)*xi*yi ]; 
             ++row; 
           }}} 
       ++submtx_counter; 
       }}} 
    plhs[0] = out; 
} 

在一個動態的版本，我不知道out_cols的價值，所以我必須要重新分配*out當上indata值的條件滿意。

我的想法是這樣的：

#include <mex.h> 

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) 
{ 
    const mxArray *I = prhs[0]; 
    double *indata = mxGetPr(I); 
    double *submtx = mxGetPr(prhs[1]); 
    const int *size = mxGetDimensions(I); 
    int xp = (int)submtx[0], yp = (int)submtx[1], zp = (int)submtx[2]; 
    int xi = size[0], yi = size[1], zi = size[2]; 

    int numsubmtx = (xi - xp + 1)*(yi - yp + 1)*(zi - zp + 1); 
    int out_rows = xp*yp*zp; 
    //int out_cols = numsubmtx; NOW UNKNOWN! 
    mxArray *out = NULL; 
    double *outdata = mxGetPr(out); 

    int submtx_counter = 0; 
    for(int z_offset = 0; ...; z_offset++){ 
     for(int y_offset = 0; ...; y_offset++){ 
       for(int x_offset = 0; ...; x_offset++){ 
        int row = 0; 
        double condition=0; 
        for(int z_counter = 0; ...; z_counter++){ 
          for(int y_counter = 0; ...; y_counter++){ 
           for(int x_counter = 0; ...; x_counter++){ 
             condition += indata[ (x_offset+x_counter) + (y_offset+y_counter)*xi + (z_offset+z_counter)*xi*yi ]/(xp*yp*zp); 
             ++row; 
           }}} 
        if(coundition>0.5){ 
         out = mxRealloc(out, (submtx_counter+1)*out_rows*sizeof(double)); 
         double *outdata = mxGetPr(out); 
         int row = 0; 
         for(int z_counter = 0; ...; z_counter++){ 
          for(int y_counter = 0; ...; y_counter++){ 
           for(int x_counter = 0; ...; x_counter++){ 
             outdata[submtx_counter*out_rows + row] = indata[ (x_offset+x_counter) + (y_offset+y_counter)*xi + (z_offset+z_counter)*xi*yi ]; 
             ++row; 
           }}} 
       ++submtx_counter; 
       } 
       }}} 
    plhs[0] = out; 
} 

有什麼不對？

Answer 1

我沒有在你的代碼的邏輯仔細地看了看，但我可以看到以下問題：

mxArray *out = NULL; 
double *outdata = mxGetPr(out); 

和

out = mxRealloc(out, (submtx_counter+1)*out_rows*sizeof(double)); 

將有奇怪的行爲。一個mxArray是一個結構，您想要爲結構指向的數據而不是結構本身重新分配內存。相反，嘗試

double *outdata = mxMalloc(out_rows*sizeof(double)); 

和

outdata = mxRealloc(outdata, (submtx_counter+1)*out_rows*sizeof(double)); 

，然後在最後，創建您的輸出矩陣：

mxArray *out = mxCreateDoubleMatrix(out_rows, submtx_counter, mxREAL); 
mxSetPr(out, outdata); 
plhs[0] = out; 

這將保證在out元數據給你的矩陣正確的大小等。