Searching structs...

Can anyone give me a general idea on searching structs in files?

For example:

Let's say I have a struct-type "flower".

PHP Code:

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struct flower{
char common_name[100];
char scientific_name[100];
char color[50];
                    }; 


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Now suppose I want to search a file filled with these structs by "common_name" so that I may obtain the "scientific_name" of that flower. Or perhaps search all structs of a certain "color" in order to print out the "common_name"s of all matching flowers.

First of all, I do not understand how, if at all, these structs are distinguished at all from simply plain data, since opening a plain-text file of a group of these structs simply shows data, without any "markings" indicating they ARE indeed structs...? Very weird.

So I am guessing I will have to master "fseek()", "ftell()", et al, in order to "impose" a distinguishability between plain data and structs stored in files, but all the books I have just gleen over this information very quickly.

Anyway, that's a long-winded explanation of this newbies current difficulties.

All, advice, examples, and dissertations are welcome, no matter how abstract!

Thanks

I have time to make a qucik reply to this. I'm not exactly sure how you would go about applying the program logic because I have some difficulty understanding the purpose of your program however I can point out a few things, maybe one of which would be helpful.

A structure is a convienient way to group data in the form of a record. So there is nothing wrong with this code of yours:

Code:

---

struct flower
{
  char common_name[100];
  char scientific_name[100];
  char color[50];
};

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But what you may also want to do is create a table of names:
char common_name[][50] = { "tulup","rose","blaa blaa"};
Now ofcourse your table would be much nicer.

Anyway a table can serve as a reference. If you had one or two pices of the record you could reference a table of names and identify say the common name or else the equivalent scientific name. Notice I used the common name for a reason!

Quote:

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Note: names can follow an alphabetical ordering such that: common_name[10] could be determined to be a "rose" for example, or common_name[20] could be a "tulup". Anyway you would be able to apply a number and get a known result. Get it? Think about this.

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I'm not sure if that is the intention of your program. As far as reading records into the structure, this can be done in a number of ways. You can create a structure of fixed length such as:

Code:

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//structure array for 30 records
struct flower Myflowers[30];

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or else you can build a linked list of structures which would allow you to join a list of records that would grow as large or as small as it needed to be based on the number of records in the datafile. It is called a self referencial structure because it requires each record to be able to form a link with another record. Another name for the records are nodes.

Code:

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typedef struct node_s
{
  char common_name[100];
  char scientific_name[100];
  char color[50];
  struct node_s *linkp;
}node_t;

---

As far as reading from a file. If it is a binary file than use fread and fwrite. If it is a text file use fscanf and fprintf. You can also use fgets.

Code:

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  struct flower Myflowers[10];
  int counter = 0;
  int status;

  FILE *fptr = fopen("a://file.txt","r");
  if (fptr == NULL) exit(1);
 
  while(counter < 10)
  {
    status = fscanf(fptr,"%s%s",
              Myflowers[counter].common_name,
              Myflowers[counter].color);
   
    //validates records read on each loop pass
      if (status != 2) break;
      ++counter;
  }
  ...

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This is the way you could go about it using a structure array.