Value Lookup from File without Slurping With Map

[gundalav]

I have a repository file (let's call it repo.txt)
that contain two columns like this:

AAA    0.2
AAT    0.3
AAC   0.02
AAG   0.02
ATA    0.3
ATT   0.7

Given another query vector for example:

vector <string> queryVec;
queryVec.push_back("AAC");
queryVec.push_back("ATT");

I would like to find the corresponding value for each query above,
yielding:

0.02
0.7

However, I want to avoid slurping whole repo.txt into an object (e.g. map).
Is there any ways to do that?

The reason I want to do that because repo.txt is very2 large size
(milions of lines,
with tag length > 30 bp), and my PC memory is too small to keep it.

[Zaita]

Database.
or iterate through the file each time you need to do a search.