fgets and breaking out of while loop

I'm trying to create a file reader for files with the following basic structure:

a INFOA2
b INFOB1
b INFOB2
c INFOC1
c INFOC2
a INFOA2

Here is what I have so far

Code:

---

while ((fgets(this, 99, fp)) != NULL)
{
    if (this[0] == 'a')
    {
          // DO THIS

          while ((fgets(this, 99, fp)) != NULL)
          {
                if (this[0] == 'b');
                else if (this[0] == 'c');
          }
    }
}

---

The problem is that in the inner for loop, if "this" is not 'b' or 'c', it should break out of loop and go to look for next 'a'. But with the current if and else if statements, it will of course just skip the next 'a' and go to the next 'b' or 'c'. How can I break out of this loop?
Probably an else statement, but what should it include? I tried an empty else...
Thanks

Why wouldn't it include "break"?

Of course the trick is that you've already read the line, and you don't want to read it again. You should use ... well, I don't know if it has a real name, but when I was learning COBOL (shudder) it was called control-break programming (shudder) -- you read each line in one loop without trying to nest things.

break! right on. thanks

Hmm, I'm still having a looping issue:

Code:

---

while ((fgets(this, 99, fp)) != NULL)
{
    if (this[0] == 'a')
    {
          // DO THIS

          while ((fgets(this, 99, fp)) != NULL)
          {
                if (this[0] == 'b')
                  // DO THAT
                else if (this[0] == 'c')
                  // DO OTHER
                else
                  break;
          }
    }
}

---

The problem is this:
If the file I am reading has
a INFOA1
b INFOB1
b INFOB2
c INFOC1
c INFOC2
a INFOA2

Then, when I run the program, I will enter inner loop after encountering first line starting with 'a'. I will then access both 'b' s, but since 'c' is an else if, I never seem to reach them.

The problem is my loop structure. Does anyone see what I'm saying and know a way to fix?
Thank you for your help.

If the code you have posted is REALLY what you are working on (rather than some extremely simplified version), it should work fine with the else if to get to the 'c' type lines.

You may need to post more realistic code if the posted code isn't EXACTLY like your real code.

--
Mats

Sorry, it is actually more like:

Code:

---

while ((fgets(this, 99, fp)) != NULL)
{
    if (this[0] == 'a')
    {
          // DO THIS

          while ((fgets(this, 99, fp)) != NULL)
          {
                if (this[0] == 'b')
                  sscanf(this, "b %i", &variable);
                else if (this[0] == 'c')
                  sscanf(this, "c %i", &variable1);
                else
                  break;
          }
    }
}

---

That should work.

--
Mats

if I have:

else
break;

It never gets to the 'c' lines but does get to every 'a' and 'b'
If I replace that else with:
else if (this[0] == 'a')
break;
Then it does get to the 'c' lines, but never reaches the second 'a'

Any idea?

Ah, hang on a bit. You read a line, then you read another line. Then you read a line with 'a' at the beginning in the inner loop, then break. You are then reading another line in the outer loop before you look at the first letter of the string - and in your posted input file, it actually would then be finished because the second 'a' line is the last one in the file.

--
Mats

Oops,
sorry again.

Should be like:
a INFOA1
b INFOB1
b INFOB2
c INFOC1
c INFOC2
a INFOA2
b INFOB3
b INFOB4
c INFOC3
c INFOC4

I modified your code a bit:

Code:

---

#include <stdio.h>

int main()
{
        FILE *fp = fopen("test.txt", "r");
        char line[99];
        char variable[99];
        char variable1[99];
        if (!fp)
        {
                fprintf(stderr, "Could not open test.txt\n");
                return 1;
        }

        while ((fgets(line, 99, fp)) != NULL)
        {
                printf("Outer Line =%s\n", line);
                if (line[0] == 'a')
                {
                        while ((fgets(line, 99, fp)) != NULL)
                        {
                                printf("Inner Line =%s\n", line);
                                if (line[0] == 'b')
                                        sscanf(line, "b %s", variable);
                                else if (line[0] == 'c')
                                        sscanf(line, "c %s", variable1);
                                else
                                        break;
                        }
                        printf("var = %s, var1 = %s\n", variable, variable1);
                }
        }
        return 0;
}

---

And I got this output, which quite clearly shows that you are skipping over the second 'a' line:

Code:

---

Outer Line =a INFOA1

Inner Line =b INFOB1

Inner Line =b INFOB2

Inner Line =c INFOC1

Inner Line =c INFOC2

Inner Line =a INFOA2

var = INFOB2, var1 = INFOC2
Outer Line =b INFOB3

Outer Line =b INFOB4

Outer Line =c INFOC3

Outer Line =c INFOC4

---

This was done as a quick hack - it's not intended as "how you go about writing good programs".

--
Mats

So, how do I work around this? Should I take you to mean that even your modification produced the same result? What might be a better way to accomplish this?

My modification is to show you what happens.

Why do you feel that you need two loops in the first place?

I personally would be very tempted to just put a switch-statement with case 'a', case 'b' and case 'c' in the outer loop, and completely remove the inner loop. But I suspect that although you say this is what your input and your actual code is, that it's still not actual code and actual input (particularly as your input is not integer values, but you are reading with %i).

How do I format a switch of (line[0] == 'a')
Thanks for all your help!

Code:

---

int main()
{
        FILE *fp = fopen("test.txt", "r");
        char line[99];
        char variable[99];
        char variable1[99];
        if (!fp)
        {
                fprintf(stderr, "Could not open test.txt\n");
                return 1;
        }

        while ((fgets(line, 99, fp)) != NULL)
        {
                printf("Line =%s\n", line);
                switch(line[0])
                {
                case 'a':
                        // Skip 'a' lines.
                        break;
                case 'b':
                        sscanf(line, "b %s", variable);
                        break;
                case 'c':
                        sscanf(line, "c %s", variable1);
                        break;
                default:
                        fprintf(stderr, "Incorrectly formed line...\n");
                        break;
                }
        }
        return 0;
}

---

Does this work?

--
Mats

Actually, switch won't work. Here is why:
I'm building a nested structure that works in the following way:

when a line starts with 'a', that starts a new "object" (not in the object-oriented sense).
then the subsequent 'b' and 'c' lines contain data pertaining to that 'a' object.
So when we reach the next 'a', the 'b' and 'c' lines will go into this object's structure.

a 1
...b 1
...b 2
...c 1
...c 2
a 2
...b 3
...b 4
...c 3
...c 4

For this reason, I need to nest. You see what I'm saying?

I see what you are saying, but without understanding more about your actual REAL code, I can't say if there's a simple way of just adding a tiny bit of code to the 'a' case, or if we really need a more complicated method of doing the work. There are ways to use two loops, but you essentially have to still detect that you read an 'a' line in the inner loop and then reuse that for the 'a' case in the outer loop, rather than reading a new line in the outer loop.

--
Mats

Can I email it to you?

Quote:

---

Originally Posted by pollypocket4eva

Can I email it to you?

---

No, I don't do private help in that way.

Are you storing the "Object" in an array or something, or what happens after you've read teh 'b' and 'c' lines? If you are storing in an array, just count up the index in to the array when you get to the 'a' line [start with index = -1].

--
Mats

Ok, here is the real thing.
Thanks!

Code:

---


                while ((fgets(line, 100, fileinput)) != NULL)
                {
                        if (line[0] == 'a')
                        {       
                                int Count1a = Count2a;
                                int Count1b = Count2b;
                               
                                while ((fgets(line, 100, fileinput)) != NULL)
                                {
                                        if (line[0] == 'b')
                                        {
                                                sscanf(line, "b %f %f %f", &v1, &v2, &v3);                 
                                                Count2a++;
                                        }
                                        else if (line[0] == 'c')
                                        {
                                                sscanf(line, "c %d %d %d", &t1, &t2, &t3);
                                                Count2b++;
                                        }
                                        else
                                        {
                                                break;
                                        }
                                }
                               
                                tab[MainCount].1f = Count1a;
                                tab[MainCount].1l = Count2a;
                                tab[MainCount].2f = Count1b;
                                tab[MainCount].2l = Count2b;
                               
                                MainCount++;
                        }
                }

---

I don't believe you.
1f, 1l, 2f, 2l are invalid names for a variable.

Be that as it may, perhaps this will work:

Code:

---

                int MainCount = -1,
                int Count1a;
                int Count1b;
...
                case 'a':
                        ++MainCount;
                        Count1a = Count2a;
                        Count1b = Count2b;
                        break;
              case 'b':
                        sscanf(line, "b %f %f %f", &v1, &v2, &v3);                 
                        Count2a++;
                        break;
// I'll let you do the rest of the work...

---

--
Mats

Hey, I just changed the variable names (for reasons of their application)... the form is exactly as I have it. Seriously.

I am grateful for your help.

Look, my question started as a "how can you nest line reading..." issue. I didn't realize it would be so far from what I had. Sorry to take your time and also to have possibly offended you by not including my actual variable names.
I don't think that implementation will work. But thanks

Quote:

---

Originally Posted by pollypocket4eva

Look, my question started as a "how can you nest line reading..." issue. I didn't realize it would be so far from what I had. Sorry to take your time and also to have possibly offended you by not including my actual variable names.

---

Right - so generally, it is a bad idea to have nested loops for reading data, for the reason you have just discovered.

It's not that I want to know whether you call your variabels fred, FirstLine or whatever, but rather that if the code doesn't actually compile I will KNOW that is NOT the code you are running on your system - and when that is the case, it's quite possible that some of the other removals will have some effect on the overall case - like we discovered here with "objects" and the fact that you are counting lines (or something) in the counters, etc, etc.

Since this is not the first case of "I've removed some essential parts of my code to hide what I'm doing and also therefore lost some important details of how the code should work", I am naturally cautious about believing someone's code that CAN NOT COMPILE. It is hard enough to get to working code without actually trying to figure out [guess] what lines of code are "important but not there".

--
Mats