Thread: A little problem with filing in C

I'm writing an SJF scheduling algo and I'm having a little problem with filing. I'm to read data from a file. I've read the entire data in a single array/pointer but now I want to read every line in a separate array/pointer/string. I'm not able to do so. Ay help would be highly appreciated.

Here's the code so far:

Code:

int main ()
{
FILE *fptr;
int i;
printf ("Output from the file");
char s[500];
int count = 0;
fptr = fopen ("file.txt","r");
if (!f)
{
return 1;
}
while (fgets(s,1000,fptr) != NULL)
printf ("%s",s);
fclose(fptr);
return 0;
}

How can I read each line in a separate array/string/pointer?

Thanks.

First you have to make an array of arrays like so:

Code:

const int MAX_ARRAY_LEN = 100;

int nr_arrays = 5;

char *array[MAX_ARRAY_LEN];

/* you have just declared a pointer to an array of length MAX_ARRAY_LEN */

/* allocate memory for an array of arrays of length MAX_ARRAY_LEN using malloc()

array = malloc((sizeof(char) * MAX_ARRAY_LEN) * nr_arrays);

/* now use array[i] to store whatever you wish */

Alright. I'm still having a few problems. I tried to get each line in a separate pointer but it's getting crazy. Here's the code:

Code:

int main ()
{
FILE *fptr;
int i;
printf ("Output from the file");
char s[500];
int count = 0;
fptr = fopen ("file.txt","r");
if (!fptr)
{
return 1;
}
while (fgets(s,1000,fptr) != NULL)
{
if (s[i] == 'P' && s[i+1] == '1')
{
while (s[i] != '\n')
{
count++;
i++;
}
}
for (for i=0; i<count; i++)
{
p1= malloc (sizeof (char)*count);
//printf ("%d", count);
p[i] = s[i];
}
printf ("%s",s);
}
for (i=0 i<count; i++)
{
printf ("%c", p1[i]);
}
fclose(fptr);
return 0;
}

PROBLEM:

The value of the counter in the loop is 4 (4 elements in the first row), and it indeed gies the value of the counter 4 when I printf the counter. But in the following loop:

Code:

for (for i=0; i<count; i++)
{
p1= malloc (sizeof (char)*count);
//printf ("%d", count);
p[i] = s[i];
}

It outputs the counter 40 times. What's going on?

I don't think that can compile, with a for on the outside and a for on the inside of the parentheses.

Would you kindly elaborate a bit more?

Originally Posted by TheUmer

Would you kindly elaborate a bit more?

Not really, no. The code you posted has a syntax error and cannot compile. Therefore that is not the code you are using. I can't help much more than say "that's not the code you're using".

????

Sorry that was a typo error. I'm compiling it on another PC and I don't have net on it.

Originally Posted by TheUmer

Sorry that was a typo error. I'm compiling it on another PC and I don't have net on it.

Well, that's fine and all, but we can't actually tell you what's going on with the code unless we can see the actual code.

What do you mean by 'actual' code?

Here's a bit modification:

Code:

while (fgets(s,1000,fptr) != NULL)
{
    if (s[i] == 'P' && s[i+1] == '1')
    {
       while (s[i] != '\n')
       {
            count++;
            p1=malloc (sizeof(char)*count);
            p1[count-1]=s[i];
            //printf ("%c", p1[i]);
            i++;
            }
        }
        for (i=0 i<count; i++)
        { 
             printf ("%c", p1[i]);
        }
        fclose(fptr);
        return 0;
}

Now the counter is running fine and it's putting values in p1, but problem is in the last loop all p1 outputs in 0 four times.

Originally Posted by TheUmer

Here's a bit modification:

Code:

while (fgets(s,1000,fptr) != NULL)
{
    if (s[i] == 'P' && s[i+1] == '1')
    {
       while (s[i] != '\n')
       {
            count++;
            p1=malloc (sizeof(char)*count);
            p1[count-1]=s[i];
            //printf ("%c", p1[i]);
            i++;
            }
        }
        for (i=0 i<count; i++)
        { 
             printf ("%c", p1[i]);
        }
        fclose(fptr);
        return 0;
}

Now the counter is running fine and it's putting values in p1, but problem is in the last loop all p1 outputs in 0 four times.

The actual code is just that, the actual code that you are running, not what you remember about your code some time later.

As to this code, it is horrific. You leak heaven knows how much memory; you keep allocating more and more space for p1 (destroying the previous values each time), and then putting just one character in the new array. Most of your p1 array will end up being --- well, not blank exactly, but containing who-knows-what.

(Of course, this analysis is only valid insofar as what you've posted matches what you've actually got -- again, there is a typo that would make this impossible to compile.)