如何直接在 C 中获取文本文件上的特定行？ （无需逐行迭代）

Question

Is there a way to get a specific line inside a text file without iterating line-by-line in C?

for example I have this text file names.txt it contains the following names below;

John
James
Julia
Jasmine

and I want to access 'Julia' right away without iterating through 'John' and 'James'?, Something like, just give the index value of '2' or '3' to access 'Julia' right away.

Is there a way to do this in C?

I just want to know how because I want to deal with a very large text file something like in about 3 billion lines and I want to access a specific line in there right away and iterating line-by-line is very slow

Answer 1

You have to at least once iterate thru all lines. In this iteration, before reading a line, you record the position in the file and save it to an array or to another file (Usually named an index file). The file shall have a fixed record size that is good for storing the position off the line in the text file.

Later, when you want to access a give line, you either use the array to get the position (Line number is the array index) or the file (You seek into the file to offset line number of record size) and read the position. Once you get the position, you can see into the text file to that position and read the line.

Each time the text file is updated, you must reconstruct the array or index file.

There are other way to do that, but you need to better explain the context.