How to allocate memory for a String Dynamically?

Question

I am trying to read Data from a Text file & storing it inside a structure having one char pointer & an int variable. During fetching data from file I know that there wil

Answer 1

If you know the position of the first structure, and the position of the second structure, you also know the total length of the first structure (position of second - position of first). You also know the size of the integer part of the structure, and therefore you can easily calculate the length of the string.

off_t pos1;  /* Position of first structure */
off_t pos2;  /* Position of second structure */

size_t struct_len = pos2 - pos1;
size_t string_len = struct_len - sizeof(int);