CODEWITHSUNDEEP
c
GBinow
GBinow

Reputation: 13

How to read a file in C and at the same time create a variable with the number of lines?

So, i need a code to read a TXT file with 5 contents each line, and store each line values in a variable. but the number of lines in the TXT will vary. so i thought of excecuting something like this:

int counter=0;
char nome="TXT NAME.txt";
 FILE *f = fopen(NAME,"r");
 do{
 if(!feof(p))
 counter++;
}while(!feof(f)); 
 fclose(f)
 int X[counter][5];

so when declaring like this, X will have the number of lines of the file. but the issue is that to store the values, i would need to open and read the file again. is there a way to save the values while declaring the variable so i dont need to open twice ?

Upvotes: 0

Views: 327

Answers (2)

chux
chux

Reputation: 153557

How to read a file in C and at the same time create a variable with the number of lines?
is there a way to save the values while declaring the variable so i dont need to open twice ?

A nice way is to read one line at a time with fgets(), copy the buffer with strdup() and save in a linked list of your creation.

Some pseudo-code to get you going.

f = open file
exit if unable to open
line_count = 0;
list = LL_Create()
char buffer[100];
while (fgets(buffer, sizeof buffer, f)) {
  Maybe special handling here to deal with lines longer than 100
  char *s = strdup(buffer);
  LL_Append(list, s);
  line_count++;
}
fclose(f);

// Use the link-list of strings

// When done
while !LL_Empty(list)
  s = LL_Pop(list)
  free(s);

LL_Destroy(list)

Upvotes: 1

AndersK
AndersK

Reputation: 36082

You can use realloc to gradually expand your "array".

But a simpler approach is to use a linked list, that way the list just grows as you read the file.

typedef struct 
{
  char data[5];
  Line* next;
} Line;

Line* first = NULL;
Line* last = NULL; 

char line[128];
while (fgets(line, sizeof(line), f)
{
  Line* tmp = malloc(sizeof(Line));
  memcpy(tmp->data,line,5);
  tmp->next = NULL;

  if (first == NULL)
  {
    first = last = tmp;
  }
  else
  {
    last->next = tmp;
    last = tmp;
  }
}

Now to go through the lines

for(Line* p = first; p != NULL; p = p->next)
{
   p->data ...
}

Upvotes: 0

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