why I am gettin a segmentation fault when using pointers

Applications Programming
1

Hello Friends,

Here is my programme.

#include <stdio.h>
 
FILE* fileopen();
void read_line(FILE*);
  
void read_line(FILE *fh){
              char s[200];
              double *input_re_see, *input_im_see;
              double input_re, input_im;

if( fgets(s,sizeof(s),fh) != NULL) { 
    sscanf(s,"%lf %lf ", &input_re, &input_im);
     
   // *input_re_see = input_re;
   // *input_im_see = input_im;
   // printf("%f  %f ", *input_re_see, *input_im_see);
 
    printf("input_re= %lf, input_im= %lf ", input_re, input_im );
    printf("%s ",s);
  }
}
FILE* fileopen(){ 
          void *file = fopen("real.dat", "r");
        if(file == NULL){
                printf("Error opening file:");
        }
       return file;
}
int main(void) { 
        
           FILE   *fh;
           int i; 
              fh = fileopen();
              for(i =0 ;i < 50 ; i++){
                 read_line(fh);
              }
 
              return 0;
}

I don't why I am gettin segmentation fault when I remove these comments..

WHat I am doing wrong with the pointer that causes segmentation fault,
Please help..

Regards,
Prady

2

You must assign the address of the variable to the pointer this way:

input_re_see = &input_re;

instead of:

*input_re_see = input_re;

Google on "pointers tutorial".

Regards

3

Thank you Franklin for encouragement ..
Actually I am learning those stuffs , and

I thought my programme is right bcoz i followed a func in a book

[code]

void swap(float *d1, float *d2){
float temp;
temp = *d1;
*d1 = *d2;
*d2 = *temp;
}
[\code]

Thats why I ve done like that.. Thanks

4

You are right ,,Now I am getting , but the problem again comes when I am trying to use a structure..
I am doing the following

typedef unsigned int U;
typedef struct {U c; U d;} vec32;
 
FILE* fileopen();
void read_line(FILE *);
 
void read_line(FILE *fh){
  char s[100];
  double input_re, input_im, *input_re_tmp, *input_im_tmp;
  U lsts, vgagain;
  U *lsts_tmp, *vgagain_tmp;
  
//vec32 *lsts_str, *vgagain_str;

   if( fgets(s,sizeof(s),fh) != NULL) {
     sscanf(s,"%lf %lf %u %u \n",&input_re, &input_im, &lsts, &vgagain);

     input_re_tmp   = &input_re;
     input_im_tmp   = &input_im;
     lsts_tmp          = &lsts;
     vgagain_tmp     =&vgagain_tmp;

    //   lsts_str->d     = &lsts;
    //   vgagain_str->d    = &vgagain;
    
 
     printf(" %f %f %u %u \n  ", *input_re_tmp, *input_im_tmp, *lsts_tmp, *vgagain_tmp);
     //printf(" %f %f %u %u %u %u %u %u \n  ", *input_re_tmp, *input_im_tmp, lsts_str->d, vgagain_str->d);
 
    }
}
FILE* fileopen(){
          void *file = fopen("abc.txt", "r");
            return file;
}
int main(void) {
 
           FILE *fh;
           int i;
              fh = fileopen();
              for(i =0;i < 5 ; i++){
                 read_line(fh);
              }
 
              return 0;
}

My Input file (abc.txt) is as follows

 5.08107 14.1132 0 71 
 -0.941856 14.9704 0 71 
 -6.80986 13.3651 0 71

Why I am getting a segmentation fault when I removing the commented lines.. Please I am elementary to pointer to structure , so If I am making some mistakes Please suggest me ..

Thanks in advance...

Regards,
Prady