How to select number of lines from large text files?

Question

I was wondering how to select number of lines from a certain text file. As an example: I have a text file containing the following lines:

branch 27 : rect id 23400
rect:   -115.475609 -115.474907
    31.393650   31.411301
branch 28 : rect id 23398
rect:   -115.474907 -115.472282
    31.411301   31.417351
branch 29 : rect id 23396
rect:   -115.472282 -115.468033
    31.417351   31.427151
branch 30 : rect id 23394
rect:   -115.468033 -115.458733
    31.427151   31.438181
Non-Leaf Node:  level=1  count=31  address=53
branch 0 : rect id 42
rect:   -115.768539 -106.251556
    31.425039   31.717550
branch 1 : rect id 50
rect:   -109.559479 -106.009361
    31.296721   31.775299
branch 2 : rect id 51
rect:   -110.937401 -106.226143
    31.285870   31.771971
branch 3 : rect id 54
rect:   -109.584412 -106.069092
    31.285240   31.775230
branch 4 : rect id 56
rect:   -109.570961 -106.000954
    31.296721   31.780769
branch 5 : rect id 58
rect:   -115.806213 -106.366188
    31.400450   31.687519
branch 6 : rect id 59
rect:   -113.173859 -106.244057
    31.297440   31.627750
branch 7 : rect id 60
rect:   -115.811478 -106.278252
    31.400450   31.679470
branch 8 : rect id 61
rect:   -109.953888 -106.020111
    31.325319   31.775270
branch 9 : rect id 64
rect:   -113.070969 -106.015968
    31.331841   31.704750
branch 10 : rect id 68
rect:   -113.065689 -107.034576
    31.326300   31.770809
branch 11 : rect id 71
rect:   -112.333344 -106.059860
    31.284081   31.662920
branch 12 : rect id 73
rect:   -115.071083 -106.309677
    31.267879   31.466850
branch 13 : rect id 74
rect:   -116.094414 -106.286308
    31.236290   31.424770
branch 14 : rect id 75
rect:   -115.423264 -106.286308
    31.229691   31.415510
branch 15 : rect id 76
rect:   -116.111656 -106.313110
    31.259390   31.478300
branch 16 : rect id 77
rect:   -116.247467 -106.309677
    31.240231   31.451799
branch 17 : rect id 78
rect:   -116.170792 -106.094543
    31.156429   31.391781
branch 18 : rect id 79
rect:   -116.225723 -106.292709
    31.239960   31.442850
branch 19 : rect id 80
rect:   -116.268013 -105.769913
    31.157240   31.378111
branch 20 : rect id 82
rect:   -116.215424 -105.827202
    31.198441   31.383421
branch 21 : rect id 83
rect:   -116.095734 -105.826439
    31.197460   31.373819
branch 22 : rect id 84
rect:   -115.423264 -105.815018
    31.182640   31.368891
branch 23 : rect id 85
rect:   -116.221527 -105.776512
    31.160931   31.389830
branch 24 : rect id 86
rect:   -116.203369 -106.473831
    31.168350   31.367611
branch 25 : rect id 87
rect:   -115.727631 -106.501587
    31.189100   31.395941
branch 26 : rect id 88
rect:   -116.237289 -105.790756
    31.164780   31.358959
branch 27 : rect id 89
rect:   -115.791344 -105.990044
    31.072620   31.349529
branch 28 : rect id 90
rect:   -115.736847 -106.495079
    31.187969   31.376900
branch 29 : rect id 91
rect:   -115.721710 -106.000130
    31.160351   31.354601
branch 30 : rect id 92
rect:   -115.792236 -106.000793
    31.166620   31.378811
Leaf Node:  level=0  count=21  address=42
branch 0 : rect id 18312
rect:   -106.412270 -106.401367
    31.704750   31.717550
branch 1 : rect id 18288
rect:   -106.278252 -106.253387
    31.520321   31.548361

I just want those lines which are in between Non-Leaf Node level=1 to Leaf Node Level=0 and also there are a lot of segments like this and I need them all.

Answer 1

The easiest method is to read as much of the file into memory, then scan for the begging token. Copy or process of all the data until the terminating token is found. Some platforms have function that hauls the file into memory for you, e.g. mmap(), although this is not in the standard language.

If the file is not changing, you could save the offsets of the token lines.

If you really need to index by line number, then create a std::map<line number, offset> variable. Read the file line by line and store the line number and offset as your read the file.