c - 使用 C : how to read cell-structure properly 读取 .mat 文件

Question

我基本上是在尝试将 Matlab 代码翻译成 C 代码。这是我之前的扩展 question .

在 Matlab 中，我使用了cell-structures，它包含可变大小的矩阵( double )。这是我的 *.mat 文件应该存储的玩具示例:

Matlab代码:

A = [[1 2 3]; [5 7 1]; [3 5 9]];
B = [[2 4];[5 7]];
Creator = 'DKumar';

nFilters = 2;

Filters{1} = [[-1.0 -1.0 -1.0]; [-1.0 8 -1.0]; [-1.0 -1.0 -1.0]];
Filters{2} = 2.0*[[-1.0 -1.0]; [-1.0 8]; [-1.0 -1.0]];

cd('/home/dkumar/CPP_ExampleCodes_DKU/Read_mat_File');
save('Test_FILE.mat', 'A', 'B', 'Creator', 'nFilters', 'Filters');

C 代码:“matread_Matrix”函数正确读取存储在 *.mat 中的矩阵。应该读取单元格结构的函数 "matread_Cell" 不工作。

#include <stdio.h>
#include <stdlib.h>
#include "/usr/local/MATLAB/R2011b/extern/include/mat.h"

mxArray *arr;
mxArray *C_CELL;
/* declare  a 2 x 1 array of pointers to access the cell array in C */
mxArray *cellArray[2];

struct stDoubleMat{
   double* pValueInField;
   int nRows, nCols;
};

void matread_Matrix(const char *file, const char *FieldName2Read, struct stDoubleMat* poDoubleMat_LOC)
{
    printf("Reading file %s...\n\n", file);

    //Open file to get directory
    MATFile* pmat = matOpen(file, "r");

    if (pmat == NULL) {
      printf("Error opening file %s\n", file);
      return;
    }

    // extract the specified variable
    arr = matGetVariable(pmat, FieldName2Read);

    double *pr;
    if (arr != NULL && !mxIsEmpty(arr)) {
        // copy data
        mwSize num = mxGetNumberOfElements(arr);

        pr = mxGetPr(arr);

        if (pr != NULL) {
        poDoubleMat_LOC->pValueInField = pr;
            poDoubleMat_LOC->nRows  = mxGetM(arr);
            poDoubleMat_LOC->nCols  = mxGetN(arr);
        }
    printf("matread_Matrix \n") ;
        printf( "oDoubleMat_LOC.nRows %i ; oDoubleMat_LOC.nCols %i \n", poDoubleMat_LOC->nRows , poDoubleMat_LOC->nCols);

    }else{
        printf("nothing to read \n") ;
    }


    // close the file
    matClose(pmat);

    return;
}

void matread_Cell(const char *file, const char *FieldName2Read, int CellIndex)
{
    printf("Reading file %s...\n\n", file);

    //Open file to get directory
    MATFile* pmat = matOpen(file, "r");

    if (pmat == NULL) {
      printf("Error opening file %s\n", file);
      return;
    }

    // extract the specified variable
    C_CELL = matGetVariable(pmat, FieldName2Read);
    cellArray[CellIndex] = mxGetCell(C_CELL, CellIndex);

    double* p2 = (double*)cellArray[CellIndex];
    int nRows  = mxGetM(cellArray[CellIndex]);
    int nCols  = mxGetN(cellArray[CellIndex]);

    printf(" From inside matread_Cell : nRows %i and nCols %i \n", nRows, nCols);

    int i2;
    for (i2 = 0; i2 < nRows*nCols; i2++)
    {
    printf(" copied value : %f \n", *p2);
    p2 = p2 +1;
    }

    // close the file
    matClose(pmat);
}


int main(int argc, char **argv)
{
    const char *FileName = "/home/dkumar/CPP_ExampleCodes_DKU/Read_mat_File/Test_FILE.mat";
    const char *FieldName2Read = "A";

    struct stDoubleMat oDoubleMat; 
    matread_Matrix(FileName, FieldName2Read, &oDoubleMat);
    double* v = oDoubleMat.pValueInField;


    printf("From main \n");
    printf( "oDoubleMat.nRows %i ; oDoubleMat.nCols %i \n", oDoubleMat.nRows , oDoubleMat.nCols);

    int i;
    for (i = 0; i < oDoubleMat.nCols*oDoubleMat.nRows; i++)
    {
        printf(" copied value : %f \n", *v);
        v = v +1;
    }

    // Reading the structure
    const char *FieldName2Read2 = "Filters";
    matread_Cell(FileName, FieldName2Read2, 0);
    matread_Cell(FileName, FieldName2Read2, 1);


    // cleanup the mex-array
    mxDestroyArray(arr);
    mxDestroyArray(C_CELL);
    /* How to delete mxArray of pointer : should this be a array of pointers */
    //mxDestroyArray(cellArray[0]);
    //mxDestroyArray(cellArray[1]);

    return 0;
}

输出:

$ gcc -g -o Test Read_MatFile_DKU_2.c -I/usr/local/MATLAB/R2011b/extern/include -L/usr/local/MATLAB/R2011b/bin/glnxa64 -lmat -lmx

$ ./Test 
Reading file /home/dkumar/CPP_ExampleCodes_DKU/Read_mat_File/Test_FILE.mat...

matread_Matrix 
oDoubleMat_LOC.nRows 3 ; oDoubleMat_LOC.nCols 3 
From main 
oDoubleMat.nRows 3 ; oDoubleMat.nCols 3 
 copied value : 1.000000 
 copied value : 5.000000 
 copied value : 3.000000 
 copied value : 2.000000 
 copied value : 7.000000 
 copied value : 5.000000 
 copied value : 3.000000 
 copied value : 1.000000 
 copied value : 9.000000 
Reading file /home/dkumar/CPP_ExampleCodes_DKU/Read_mat_File/Test_FILE.mat...

 From inside matread_Cell : nRows 3 and nCols 3 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
Reading file /home/dkumar/CPP_ExampleCodes_DKU/Read_mat_File/Test_FILE.mat...

 From inside matread_Cell : nRows 3 and nCols 2 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 
 copied value : 0.000000 

此外，我也无法正确读取此字段:Creator = 'DKumar';

更新:

根据@Sherwin 的建议

我的 C 代码:

#include <stdio.h>
#include <stdlib.h>
#include "/usr/local/MATLAB/R2011b/extern/include/mat.h"

mxArray *arr;
mxArray *C_CELL;
/* declare  a 2 x 1 array of pointers to access the cell array in C */
mxArray *cellArray[2];

struct stDoubleMat{
   double* pValueInField;
   int nRows, nCols;
};


void matread_Matrix(MATFile* pmat , const char *FieldName2Read, struct stDoubleMat* poDoubleMat_LOC)
{
    // extract the specified variable
    arr = matGetVariable(pmat, FieldName2Read);

    double *pr;
    if (arr != NULL && !mxIsEmpty(arr)) {
        // copy data
        mwSize num = mxGetNumberOfElements(arr);

        pr = mxGetPr(arr);

        if (pr != NULL) {
        poDoubleMat_LOC->pValueInField = pr;
            poDoubleMat_LOC->nRows  = mxGetM(arr);
            poDoubleMat_LOC->nCols  = mxGetN(arr);
        }
    printf("matread_Matrix \n") ;
        printf( "oDoubleMat_LOC.nRows %i ; oDoubleMat_LOC.nCols %i \n", poDoubleMat_LOC->nRows , poDoubleMat_LOC->nCols);

    }else{
        printf("nothing to read \n") ;
    }
    return;
}

void matread_String(MATFile* pmat , const char *FieldName2Read)
{
    // extract the specified variable
    arr = matGetVariable(pmat, FieldName2Read);

    double *pr;
    if (arr != NULL && !mxIsEmpty(arr)) {
        // copy data
        mwSize num = mxGetNumberOfElements(arr);
        pr = mxGetPr(arr);

        if (pr != NULL) {
            char *p2 = (char*) pr; 

            // Printing and checking
        int i2;
        for (i2 = 0; i2 < num; i2++)
        {
        printf(" copied value : %s \n", p2);
        p2 = p2 +1;
        }

    }

    }else{
            printf("nothing to read \n") ;
    }
    return;
}

void matread_Cell(MATFile* pmat , const char *FieldName2Read, int CellIndex)
{

    // extract the specified variable
    C_CELL = matGetVariable(pmat, FieldName2Read);
    cellArray[CellIndex] = mxGetCell(C_CELL, CellIndex);

    double *p2 = (double*) mxGetPr(cellArray[CellIndex]); 
    int nRows  = mxGetM(cellArray[CellIndex]);
    int nCols  = mxGetN(cellArray[CellIndex]);

    printf(" From inside matread_Cell : nRows %i and nCols %i \n", nRows, nCols);

    int i2;
    for (i2 = 0; i2 < nRows*nCols; i2++)
    {
    printf(" copied value : %f \n", *p2);
    p2 = p2 +1;
    }
}


int main(int argc, char **argv)
{
    const char *FileName = "/home/dkumar/CPP_ExampleCodes_DKU/Read_mat_File/Test_FILE.mat";
    const char *FieldName2Read = "A";

    //Open file to get directory
    printf("Reading file %s...\n\n", FileName);
    MATFile* pmat = matOpen(FileName, "r");

    if (pmat == NULL) {
      printf("Error opening file %s\n", FileName);
      return;
    }

    struct stDoubleMat oDoubleMat; 
    matread_Matrix(pmat, FieldName2Read, &oDoubleMat);
    double* v = oDoubleMat.pValueInField;

    int i;
    for (i = 0; i < oDoubleMat.nCols*oDoubleMat.nRows; i++)
    {
        printf(" copied value : %f \n", *v);
        v = v +1;
    }

    // Reading the structure
    const char *FieldName2Read2 = "Filters";
    matread_Cell(pmat, FieldName2Read2, 0);
    matread_Cell(pmat, FieldName2Read2, 1);

    // Reading the string
    const char *FieldName2Read3 = "Creator";
    matread_String(pmat, FieldName2Read3);

    // cleanup the mex-array
    mxDestroyArray(arr);
    mxDestroyArray(C_CELL);

    /* How to delete mxArray of pointer : should this be a array of pointers */
    //mxDestroyArray(cellArray[0]);
    //mxDestroyArray(cellArray[1]);


    // close the file
    matClose(pmat);

    return 0;
}

输出:

oDoubleMat.nRows 3 ; oDoubleMat.nCols 3 
 copied value : 1.000000 
 copied value : 5.000000 
 copied value : 3.000000 
 copied value : 2.000000 
 copied value : 7.000000 
 copied value : 5.000000 
 copied value : 3.000000 
 copied value : 1.000000 
 copied value : 9.000000 
 From inside matread_Cell : nRows 3 and nCols 3 
 copied value : -1.000000 
 copied value : -1.000000 
 copied value : -1.000000 
 copied value : -1.000000 
 copied value : 8.000000 
 copied value : -1.000000 
 copied value : -1.000000 
 copied value : -1.000000 
 copied value : -1.000000 
 From inside matread_Cell : nRows 3 and nCols 2 
 copied value : -2.000000 
 copied value : -2.000000 
 copied value : -2.000000 
 copied value : -2.000000 
 copied value : 16.000000 
 copied value : -2.000000 
 copied value : D 
 copied value :  
 copied value : K 
 copied value :  
 copied value : u 
 copied value :  
 copied value :  

问题:1) creator 中存储的字符串值没有正确显示。

2) 如何删除cellArray[2])？

Answer 1

事实证明，稍作改动，您的代码就可以工作了:

在函数“void matread_Cell”中，将行 double* p2 = (double*)cellArray[CellIndex]; 替换为:

p2 = (double*) mxGetPr(cellArray[CellIndex]); 

我查过了。它完成了工作。

同样要读取创建者字段，类似于 mtread_matrix 的代码应该可以工作，只是类型是 char* 而不是 double* (不过我没有检查这个。如果它不起作用请告诉我)。

更新:您可以使用以下代码读取字符串。 (引用:here)

void matread_string(const char *file, const char *FieldName2Read, char *pr, mwSize *len)
{
    printf("Reading file %s...\n\n", file);

    //Open file to get directory
    MATFile* pmat = matOpen(file, "r");

    if (pmat == NULL) {
      printf("Error opening file %s\n", file);
      return;
    }

    // extract the specified variable
    arr = matGetVariable(pmat, FieldName2Read);

    if (arr != NULL && !mxIsEmpty(arr)) {
        // copy data
        mwSize num = mxGetNumberOfElements(arr);

        //int mxGetString(const mxArray *pm, char *str, mwSize strlen);
        int res= mxGetString(arr, pr, num+1); //strlen should be len+1. c.f. reference.
        if(res==0)
            printf("success!\n");
        else
            printf("failed.\n");


        if ( pr == NULL){
            printf("null pointer.\n");
        }   
        printf("matread_string \n") ;
        printf( "len: %i \n", (int)num);

        *len=num; 

    }else{
        printf("nothing to read \n") ;
    }
    // close the file
    matClose(pmat);

    return;
}

在 main 中，您可以像这样使用它:

 const char *FieldName2Read3 = "Creator";
    char pr[20];
    mwSize len;
    matread_string(FileName, FieldName2Read3, pr, &len);

    //int i;
    printf(" copied value: %s \n",pr);
    for (i = 0; (mwSize) i <  len; i++)
    {
        printf(" copied value : %c \n", pr[i]);
    } 

关于取消分配 cellArray，我收到错误消息:“未分配正在释放的指针”，因此我认为您不需要释放它。另一个释放动态内存的有用命令是:void mxFree(void *ptr);

关于 mexPrintf 函数，我实际上可以使用它。我刚刚收到警告 implicit declaration of function 'mexPrintf' is invalid in C99 [-Wimplicit-function-declaration]，因为我是通过 gcc 而不是 mex 编译的。如果您使用的是 gcc，您可能需要包含正确的库来识别该函数。你可能会发现 this很有用，因为它对我有用。