Accesing two different rows simultaneously in C -

suppose have data set arranged in following way

19 10 1 1 12 15 1 1 13 12 4 5 10 5  2 3 ... 

and on, @ particular iteration in loop have read 1st , 4th row , in next iteration have access other set of rows,for example

1st iteration:  1st row: 19 10 1 1 4th row: 10 5  2 3  

i access data using fscanf() function. how ensure choose 1st , 4th rows or 2 rows matter @ given iteration?

(i have not considered reading 2d array since size of data set 10^8 )

thank you.

as read through data (say, stored in standard file), byte offsets rows looking row delimiters (a newline character). can read out rows based on start , end byte offset c pointer arithmetic on file * , fseek(). storing few byte offsets (an 8 byte long or equivalent, often) cheap.