CODEWITHSUNDEEP
c
user1336997
user1336997

Reputation: 105

how to save a value from pointer into a char array?

I have a file with data like this

{0 /Data1/ , 0x00, 0, 0xFF},

{1 /data2/ , 0x00, 0, 0xFF},

{2 /data3/ , 0x00, 0, 0xFF},

{3 /data4/ , 0x00, 0, 0xFF}, ...

I want to print only the second column of each line. Below is the code I worked on. 

#include<stdio.h>
#include<string.h>
int main ()
{
char filename[] = "file.txt";
FILE *file = fopen(filename, "r");
if(file!= NULL)
{
char line[128];
char * word1;
char  word2;
char  word3;
int i=0;
clrscr();
while ( fgets( line, sizeof line, file)!= NULL)
{
i=0;
word1 = strtok(line, " ,");

while(word1!= NULL)
{
i++;
if(i==2 ){

printf("%s\n",word1);
}
word1 = strtok(NULL," ,");
}

}
fclose(file);
}
else
{
perror(filename);
}


getch();

return 0;
}

it works fine. Can I save the value Im printing in each line into an array? I tried something like this

if(i==2){
word2 = * (word1);
} 
printf("%s\n",word1);

But it give me a null pointer assignment. How to store the values Im printing into an array?

Upvotes: 1

Views: 3223

Answers (3)

Jack
Jack

Reputation: 16724

Try something like this:

#define MAX_BUFFER_SIZE 256
/* ... */

char ** lines = malloc(MAX_BUFFER_SIZE + 1);
char ** p = lines;
char ** newbuf;
int len;
int bytesloaded = 0;  
int buf_size = MAX_BUFFER_SIZE;  
assert(lines != NULL);
//... loop etc.. 

if(i==2 ){
   len = strlen(word1);
   bytesloaded += len;

   if(bytesloaded >= buf_size) /* Controls buffer size. For avoid buffer overflow/heap corruption/UB. */
   {
      buf_size += MAX_BUFFER_SIZE;
      newbuf = realloc(lines, buf_size);

      if(!newbuf)  /* return or break. */ 
      {  
        printf("Allocation failed.\n");
        free(lines);
        return 1;
      }

       lines = newbuf;
    }

    *p++ = word1; /* store the word in lines */
    printf("%s\n",word1);
}

Note: Don't forget to put the 0-terminator,\0, in array, after end of first loop.

I haven't tested this code,but I believe that it works.

It a simple example how to do: a dynamic memory allocation,control the size of it,memory re-allocation and values storage.

Upvotes: 0

David Rodrigues
David Rodrigues

Reputation: 842

You are saving only the first char of string word1 into word2.

If you want store all 2nd columns you need to alloc a dynamic array of pointers to (char *) and then to each word/column alloc space to the word and copy with a strcpy because word1 is changing on each iteration of while so you can't save only the refence.

Upvotes: 1

Niklas Hansson
Niklas Hansson

Reputation: 473

You could use a dynamically allocated array, which you grow as you need more space. See Why does a large variable length array has a fixed value -1 even if assigned to in C? for more help.

Upvotes: 0

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