```
void matrix_writebinary(struct matrep *mat) {
int i,j;
FILE *fptr;
if((fptr=fopen("matrixA.bin","wb"))==NULL)
{
puts("Cannot Open File");
}
fwrite(&mat->rows,sizeof(int),1,fptr);
fwrite(&mat->cols,sizeof(int),1,fptr);
fwrite(mat->matrix,sizeof(double),(mat->rows*mat->cols),fptr);
fclose(fptr);
}
/***********************************************************/
double *matrix_readbinary(struct matrep *mat) {
int i,j;
FILE *fptr;
if((fptr=fopen("matrixA.bin","rb"))==NULL)
{
puts("Cannot Open File");
}
fread(&mat->rows,sizeof(int),1,fptr);
fread(&mat->cols,sizeof(int),1,fptr);
mat->matrix = (double *) malloc( sizeof( double ) * (mat->rows*mat->cols) ) ;
fread(mat->matrix,sizeof(double),(mat->rows*mat->cols),fptr);
fclose(fptr);
return mat->matrix;
}
```

I am using the above two functions to write a matrix to a binary file, and then read the matrix back from the file using fread.

Then I am printing the matrix, but every time I do, the first 9 elements of the matrix are zero, no matter what size mat.rows or mat.cols are, always 9 empty elements or -1.#R when trying to print, so I think that fread(val,sizeof(double),(mat->rows*mat->cols),fptr);

is reading in 9 bad doubles but I have no idea why...

In the main(), the user specifies the row and col size etc.

If someone could explain why I would really appreciate it.

Here is the func used to print

```
void print_matrix( struct matrep *mat )
{
double *ptr ;
int i, j ;
ptr=mat->matrix;
if ( mat->matrix==0 || mat->rows==0 || mat->cols==0 )
{
printf("\n\nEmpty matrix" );
return ;
}
printf( "\n\nrows %d, columns %d\n\n", mat->rows, mat->cols) ;
for ( i=0; i < mat->rows; i++ )
{
for ( j=0; j < mat->cols; j++ )
{
printf( "%5.2lf\t", *ptr++ );
}
printf( "\n" ) ;
}
}
```

and the structure used...

```
struct matrep {
int rows,cols;
double *matrix;
};
struct matrep MATRIX,MATRIX1;
```

code that call matrix_readbinary() in main()

```
//BINARY WRITE/READ
printf("\nWriting binary data now...\n");
matrix_writebinary( &MATRIX ) ;
_flushall();
getchar();
printf("\nReading binary data now...\n");
MATRIX1.matrix=matrix_readbinary(&MATRIX1 ) ; // reads above matrix from file as a copy
if(MATRIX1.matrix!=NULL){
printf("\nPrinting read .bin...\n");
print_matrix(&MATRIX1 ) ; // prints this copyed matrix
}
```

I created a test app under Windows with Visual Studio using your posted code and it worked fine.

```
#include <stdio.h>
#include <tchar.h>
#include <string.h>
#include <stdlib.h>
struct matrep
{
int rows,cols;
double *matrix;
};
void matrix_writebinary(struct matrep *mat)
{
int i,j;
FILE *fptr;
if((fptr=fopen("matrixA.bin","wb"))==NULL)
{
puts("Cannot Open File");
}
fwrite(&mat->rows,sizeof(int),1,fptr);
fwrite(&mat->cols,sizeof(int),1,fptr);
fwrite(mat->matrix,sizeof(double),(mat->rows*mat->cols),fptr);
fclose(fptr);
}
/***********************************************************/
double *matrix_readbinary(struct matrep *mat)
{
int i,j;
FILE *fptr;
if((fptr=fopen("matrixA.bin","rb"))==NULL)
{
puts("Cannot Open File");
}
fread(&mat->rows,sizeof(int),1,fptr);
fread(&mat->cols,sizeof(int),1,fptr);
mat->matrix = (double*) malloc(sizeof(double)*(mat->rows*mat->cols));
fread(mat->matrix,sizeof(double),(mat->rows*mat->cols),fptr);
fclose(fptr);
return mat->matrix;
}
void print_matrix( struct matrep *mat )
{
double *ptr ;
int i, j ;
ptr=mat->matrix;
if ( mat->matrix==0 || mat->rows==0 || mat->cols==0 )
{
printf("\n\nEmpty matrix" );
return ;
}
printf( "\n\nrows %d, columns %d\n\n", mat->rows, mat->cols) ;
for ( i=0; i < mat->rows; i++ )
{
for ( j=0; j < mat->cols; j++ )
{
printf( "%5.2lf\t", *ptr++ );
}
printf( "\n" ) ;
}
}
struct matrep MATRIX,MATRIX1;
int _tmain(int argc, _TCHAR* argv[])
{
int r;
int c;
double* pdbl;
MATRIX.rows = 4;
MATRIX.cols = 3;
pdbl = (double*) malloc(sizeof(double) * MATRIX.rows * MATRIX.cols);
MATRIX.matrix = pdbl;
for ( r = 0; r < MATRIX.rows; ++r )
{
for ( c = 0; c < MATRIX.cols; ++c )
{
*pdbl++ = c + r;
}
}
matrix_writebinary(&MATRIX);
print_matrix(&MATRIX);
matrix_readbinary(&MATRIX1);
print_matrix(&MATRIX1);
}
```