CODEWITHSUNDEEP
lua
Kan
Kan

Reputation: 169

Read a file in a specific line

I have a txt file which stores data in the following format:

300
400
500
600

I was trying to read this file in a specific line, e.g. read(".txt",2) will return 500, I also try the following 

cell.T = {}  -- temperatures, K (as a table)
filename = "input.txt"
fp = io.open( filename, "r" )
local n=0
for line in fp:lines() do
   n = n+1
   if n == index_number then
       cell.T[0]=line;
       break;
   end
end 
fp:close()

My index_number is 0 1 2 3 respectively, but what I get is 0 300 400 500

something elsewhere should be wrong, but I don't know how to figure it out, can anyone have a look at this file?

Upvotes: 2

Views: 162

Answers (1)

legends2k
legends2k

Reputation: 32894

The index_number variable starts with 0, but the code

local n=0
for line in fp:lines() do
   n = n+1
   if n == index_number then  -- this condition will never be met when n = 0

shows that n will never be 0 since it's incremented just before the check. Make the initialization like this

local n = -1

Or idiomatically, as indices start at 1 in Lua, you could change it to a post-increment

local n = 0
for line in fp:lines() do
    if n == index_number then
        -- do stuff
    end
    n = n + 1
end

Upvotes: 2

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