Help on reading from a file.

I am trying to write a program (in C) for reading grid1.dat and grid2.dat and displays the data it has read on the screen.

I have got as far as the program listed below, it seems to compile fine but doesn’t seem to read correctly as most of the time a runtime error occurs. I’m also unsure how to implement the fprintf statement to get the data to be displayed on the screen.

Any help or advice would be greatly appreciated.

Many thanks

James.


Info stored in grid1.dat:

id x y
1 1.2 0.8
2 1.2 1.0
3 1.2 1.2
4 1.4 0.8
5 1.4 1.0
6 1.4 1.2
7 1.6 0.8
8 1.6 1.0
9 1.6 1.2


Info stored in grid2.dat:

id x y
1 1.2 0.8
2 1.2 1.0
3 1.2 1.2
4 1.4 0.8
5 1.4 1.0
6 1.4 1.2
7 1.6 0.8
8 1.6 1.0
9 1.6 1.2
10 1.8 0.8
11 1.8 1.0
12 1.8 1.2

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
char line[101], filename[101];
char*line_ptr;
struct node
        {
        int id;
        double x, y;
        };
struct node node_array[100];
int no_nodes = 0, no_values;
FILE*input_stream;
fprintf(stdout, "Enter file name:");
fscanf(stdin, "%s", filename);
if ((input_stream = fopen(filename, "r")) !=NULL)
        {
        fgets(line, sizeof(line), input_stream);
        while(((line_ptr = fgets(line, sizeof(line), input_stream)) !=NULL)&&
                  ((no_values = sscanf(line, "%d %lf %lf",
                                                          &node_array [no_nodes].id,
                                                          &node_array [no_nodes].x,
                                                          &node_array [no_nodes].y)) = =3)) no_nodes++;


if ((line_ptr !=NULL)&&(no_values !=3))
        fprintf(stdout, "Error reading line %s\n", line);
else
        if(line_ptr= =NULL)
          fprintf(stdout, "End of file found\n");
}
}

---

> as most of the time a runtime error occurs
And saying what that was would be a big help...

Well your while loop is overly complex, you're doing too much in the conditional part and leaving the statement almost empty

Additionally, you're not range checking your node_array array indices.

Code:

---

while ( fgets(line, sizeof(line), input_stream) != NULL ) {
    no_values = sscanf(line, "%d %lf %lf",
        &node_array [no_nodes].id,
        &node_array [no_nodes].x,
        &node_array [no_nodes].y);
    if ( no_values == 3 && no_nodes < 100 ) {
        no_nodes++;
    } else {
        break;
    }
}
if ( feof(input_stream) ) {
    // normal EOF
} else
if ( ferror(input_stream) ) {
    // read error
} else
if ( no_values != 3 ) {
    // conversion error
} else
if ( no_nodes == 100 ) {
    // array full
}

---

> I’m also unsure how to implement the fprintf statement to get the data to be displayed on the screen.
Hard to believe you got this far with sscanf without knowing at least how to try it.

hi,

i think i have solved ur problem. ur problem if i have understood is how to use fprintf in ur code. it is very simple buddy just some kind of a logic is required and u can do it......

ur whole code goes like this..............

Code:

---


#include <stdio.h>
#include <stdlib.h>

int main(void)
{
        char line[101], filename[101];
        char*line_ptr;
        struct node
        {
                int id;
                        double x, y;
        };
       
        struct node node_array[100];
        int no_nodes = 0, no_values=0;
        FILE*input_stream;

        fprintf(stdout, "Enter file name:");
        fscanf(stdin, "%s", filename);

        if ((input_stream = fopen(filename, "r")) !=NULL)
        {
                fgets(line, sizeof(line), input_stream);
                while((line_ptr = fgets(line, sizeof(line), input_stream))!=NULL)
        {
          if((no_values = sscanf(line, "%d %lf %lf",&node_array [no_nodes].id,&node_array [no_nodes].x,&node_array [no_nodes].y))==3)
          {
              no_nodes++;
          }
          if ((line_ptr !=NULL)&&(no_values !=3))
            fprintf(stdout, "Error reading line %s\n", line);
          else if(line_ptr==NULL)
                  fprintf(stdout, "End of file found\n");
          else
              fprintf(stdout,"%d %lf %lf\n",node_array [no_nodes-1].id,node_array [no_nodes-1].x,node_array [no_nodes-1].y);
        }
    }
    system("pause");
}

---

i think this will work for u and hope i i have solved ur problem sucessfully

bye
Praveen

> i think this will work for u and hope i i have solved ur problem sucessfully
It's "you" and "your"