Thread: Reading Certain Lines In File?

I am making a database type program that keeps track of people. For example, employees. You can edit, add, or delete each person. My problem is reading specified lines and adding them to a listbox. Here's the file format:


\Jon Doe
Address: 123 ABC Ln.
-
\Jane Doe
Address: ABC 123 Ln.
-


How do I read the lines with just the \Name Here on them and add them to the listbox?

IMHO you should open, read the whole file to memory and close it (unless is very big ie 10Mb+). Do not reopen unless need to change data.

Copy the data to an array of structures of the same format as the original data. Use a index file or linked list if large amounts of data.

Otherwise need to look for the '/' in the file. Test the string after it with strcmp() or or strstr() and then edit it.

Beware of editing text files as the size of strings varies (where as a struct saved as binary does not).

Using structs would be a good and organized way, but very memory consuming. I suggest novacain's second idea by just reading the file into a buffer and going through each line (with fgets) and testing to see if it has a '/' in front of the line. If you are looking for space conservation, do this. If you are looking for time conservation, use structs. It's up to you...

I am only familiar with fstream, but I know some about fgets(). Could you show a small example of using fgets() to do this?

...

Let's say you're using the stdio lib (some incomplete code just to show you implementation):

Code:

fp = fopen(szFileName, "r");

while (fgets(line, sizeof(line), fp) != NULL)
{
    if (line[0] == '/')
        process the name
    else
        continue;
}

This (untested) code is pretty much how you want to go about it. Just check your string from getting the line from the file to see if it meets your requirements.

I tried this:


dbFile = fopen("emplist.txt", "r");

while (fgets(names, sizeof(names), dbFile) != NULL)
{
if (names[0] == '/')
{
do
{
fgets(names, sizeof(names), dbFile);
} while (names[0] == '\n');
}
}


SendMessage(dbList, LB_ADDSTRING, (LPARAM)100, (WPARAM)names);


And it just gets the last line in the file. What did I do wrong?

The reason for just getting the last line of the file in the listbox is because you reading in another line even when you already found a valid name line. In other words, you don't have to reread the line in. You are just incrementing the file counter and causing a problem (which is causing it to go to the last line, making it in the listbox). Here is the corrected code:

Code:

dbFile = fopen("emplist.txt", "r"); 

while (fgets(names, sizeof(names), dbFile) != NULL) 
{ 
if (names[0] == '/') 
{ 
names[strlen(names)-1] = '\0'; // get the '\n' char out of the string
SendMessage(dbList, LB_ADDSTRING, (LPARAM)100, (WPARAM)names); 
} 
}

This should logically do it. You find a valid string (with the if test) and it's valid, so enter it in the listbox. Understand? Any more questions?

How big is the data file?

I would always use structs. Easier to read, pass and mem manage.

You can read the file, fill in the structs and save to a binary file, say
DB_STRUCT
char sFirstName[64];
char sSurName[64];
char sAddress[128];
long lPhoneNum;
ect

Then all you have to do is find the size of the file with GetFileSize(), divide thias by the size of a struct to get the number of records. You can then dynamicly alloc the mem with GlobalAlloc(), GlobalLock() it and read the file for sizeof(DB_STRUCT) record by record (or pick it up in one read to increase speed).
Stack the LB using the struct. At close GlobalHandle() and GlobalFree() the mem.

This is heaps easier in the long run. Even if your struct is say 20Kb (as the one I am using is for over 600 records is) dynamic mem alloc is not a problem.

If you don't you could run into the problem I had trying to hack a 'Serious Sam' file. One small change in a file (changed 5 chars to 4) and it then told me it needed approx 12Gb of mem to run!