How to read a specific line from a text file in c++?

Question

C++ program that displays on the screen item codes with corresponding item descriptions and prices. It asks the user to enter the code of the item purchased by a customer. It looks for a match of the item code stored in items.txt.

How can I output only a specific line from a text file after the user inputs the item code?

Answer 1

You need to read the file line-by-line (std::getline), extract (depending on the exact format, e.g. by searching for a whitespace in the string) and compare the code and then return the corresponding line on a match.

It is not possible to access lines from a text file directly by index or content.

This is assuming that you mean the file contains lines in the form

code1 item1
code2 item2
//...

If the code is just the index of the line, then you only need to call std::getline in a loop with a loop counter for the current index of the line.

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If you do this multiple times on the same file, you should probably parse the whole content first line-by-line into a std::vector<std::string> or a std::(unordered_)map<std::string, std::string> or something similar to avoid the costly repeated iteration.

Depending on the use case, maybe it would be even better to parse the data into a database first and then query the database, even if it is only e.g. sqlite or something like that.