Thread: Access Violation (segmentation fault) issues with an array ?

Hey I'm writing a programme to create a random matrix and print it to a file. But when I run it just shuts the programmes down. No errors no warnings nothing.
I'm using Dev C++ and when I debug I get an error "access violation (segmentation violation).
I've tested the file out put and it works I've also tested the print_matrix function and it works.
The issue lies in the rand_matrix function, I've done a bit of research and I think the issue is indexing outside an array or miss-indexing

Any help is help
Thanks in Advance

Code:

#include <stdio.h>#include <stdlib.h>
#include <time.h>
#include <malloc.h>
#include <conio.h>


typedef struct matrep {
        unsigned rows, columns;
        double*data;
        } MATRIX;


/////////////////////////////////////////////////////////
double random()
{
    static int seeded = 0;
    double val ;
    if ( !seeded )
        {
         srand( time(NULL) ) ;
         seeded = 1;
        }
    val = ((double)rand())/ (double)RAND_MAX * 100.0 ;
    return val ;
}
////////////////////////////////////////////////////////
MATRIX*rand_matrix( struct matrep*mat ) 
{
   for ( int i=0; i < mat->rows; i++ )
       {
        for ( int j=0; j < mat->columns; j++ )
             {
             *(mat->data)++ = random() ;
             }
        }
  return mat ;
}
//////////////////////////////////////////////////////////
void print_matrix(struct matrep*mat ) 
{
  int i, j ;


   if ( (mat->data)==0 || (mat->rows)==0 || (mat->columns)==0 )
       {
       printf("Empty matrix\n" );
       return ;       
        }
    printf( "\n\nMatrix of dimensions %d x %d\n\n", mat->rows, mat >columns) ;


   for ( i=0; i < mat->rows; i++ )
        {
        for ( j=0; j < mat->columns; j++ )
             {
              printf("\t%1.2lf", *(mat->data)++ );
              }
        printf("\n") ;
         }
             
}
///////////////////////////////////////////////////////////
void matrix_write(struct matrep*mat,FILE *fp)
{
    fprintf(fp,"rows = %d, columns = %d \n",mat->rows,mat->columns);
    for ( int i=0; i < mat->rows; i++ )
        {
        for ( int j=0; j < mat->columns; j++ )
            {
            fprintf(fp, "\t%.2lf", *(mat->data)++ );
            }
        fprintf(fp, "\n" ) ;
         }
}


int main()
{


    MATRIX mat;

    mat.rows=4;
    mat.columns=5;

    MATRIX *ptr;
    ptr=&mat;


    rand_matrix(ptr);
    print_matrix(ptr);


     FILE *fp;
     char file[80];

    printf("enter file name: ");
    gets(file);
   
    if((fp=fopen(file,"w"))==NULL)
       { 
       printf("Cannot open file %s",file);
       getch();
       exit(1);
        }
    matrix_write(&mat,fp);
    fclose(fp);

    printf("\nOperations complete. Hit any key to exit");
 

    getch();
    return (0);           
}

You haven't allocated any memory for structure element "data".
Plus it's not a good idea to increment and lose value of the pointer.