Re: Reading Particular contents from file

[Tom N Harris <telliamed@...>]

On 01/25/2012 09:21 AM, Sandeep Ghai wrote:
> Hello everyone,
> I am doing file handling using Lua programming. But I need some help
> where I got stuck.
> I want to read particular line from the file.
> consider the following file:-
...
> I want to read 'x',and 'y' values whenever I pass argument to read
> 'nodes' and similarly for other contents(like constraint,forces etc) too.
> After then I want to pass all these things directly into database,to
> gather all the similar things from number of files.
> Please help me in syntax. I am a beginner in Lua Programming.
> Thank you in advance.

While the more professional thing to do would be to use LPEG, this is a 
fast and only slightly error-prone way to get it done with string.match 
and tail-calls as a state machine. Call parse_data_description with a 
file handle and it will produce a table. Then move it into the database 
with whatever backend you're using. I guessed at what fields may be 
optional, so you'll want to tweak the 'material or "beam"' like expressions.


local headings

local function parse_problem_description(T, F)
    local line = F:read()
    if not line then
        return T
    end
    if headings[line] then
        return headings[line](T, F)
    end
    local title = string.match(line, '^title="([^"]*)"')
    if title then
        T.title = title
    end
    return parse_problem_description(T, F)
end

local function parse_nodes(T, F)
    local line = F:read()
    if not line then
        return T
    end
    if headings[line] then
        return headings[line](T, F)
    end
    local i,x,y = string.match(line, '^(%d+) +x=(%d+) +y=(%d+)')
    if i then
        i,x,y = tonumber(i),tonumber(x),tonumber(y)
        local constraint = string.match(line, 'constraint=(%a+)')
        local force = string.match(line, 'force=(%a+)')
        T.nodes[i] = {
            x = x,
            y = y,
            constraint = constraint or 'free',
            force = force
        }
    end
    return parse_nodes(T, F)
end

local function parse_beam_elements(T, F)
    local line = F:read()
    if not line then
        return T
    end
    if headings[line] then
        return headings[line](T, F)
    end
    local i,n1,n2 = string.match(line, '^(%d+) +nodes=%[(%d+),(%d+)%]')
    if i then
        i,n1,n2 = tonumber(i),tonumber(n1),tonumber(n2)
        local material = string.match(line, 'material=(%a+)')
        T.elements[i] = {
            nodes = {n1,n2},
            material = material or 'beam'
        }
    end
    return parse_beam_elements(T, F)
end

headings = {
    ['problem description'] = parse_problem_description;
    ['nodes'] = parse_nodes;
    ['beam elements'] = parse_beam_elements;
}

function parse_data_description(F)
    local T = { title="", nodes = {}, elements = {} }
    return parse_problem_description(T, F)
end


--
- tom
telliamed@whoopdedo.org