Passing value of JSON data to variable
lazarus / 38-Networking and Web Programming

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CyberFilth · 2015-04-01 15:41

Hi, I'm trying to get back into Pascal after a...20 year hiatus. I'm
trying to familiarise myself with the syntax again by putting together
a simple currency conversion program that grabs the current exchange
rates from http://fixer.io/ in JSON format.
So far, I can download and display the exchange rate.
What I can't seem to do is pass the exchange rate into a variable.

This is what I have so far:
Code: [Select]{$mode objfpc}{$H+}

uses fphttpclient, fpjson, jsonparser;

Var
  S : String;
  J: TJSONData;
  initialAmount, endAmount, rate: real;

begin
  With TFPHttpClient.Create(Nil) do
    try
      S:=Get('http://api.fixer.io/latest?base=GBP');
    finally
      Free;
    end;
    J:= GetJSON(S);
    writeln ('Current exchange rate of GBP to Polish złoty:
',J.FindPath('rates.PLN').AsFloat:2:2);
end.

This gets the exchange rate from GBP to Polish złoty and prints it to
the screen. It works fine but what I want to do next is something
along the lines of:
Code: [Select]rate := J.FindPath('rates.PLN').AsFloat:2:2;
writeln;
write ('Enter initial amount in GBP £');
readln (initialAmount);
endAmount := initialAmount * rate;
writeln (endAmount);   

...and that's where my memory is kinda letting me down. I've read
through the examples for parsing JSON but I can't seem to find a
solution.

Any suggestions?

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taazz · 2015-04-01 16:46

Code: [Select]{$mode objfpc}{$H+}

uses fphttpclient, fpjson, jsonparser;

Var
  S : String;
  J: TJSONData;
  initialAmount, endAmount, rate: real; // or single or Double

begin
  With TFPHttpClient.Create(Nil) do
    try
      S:=Get('http://api.fixer.io/latest?base=GBP');
    finally
      Free;
    end;
    J:= GetJSON(S);
    rate := J.FindPath('rates.PLN').AsFloat;
    writeln ('Current exchange rate of GBP to Polish złoty:
',rate:2:2);
    writeln;
    write ('Enter initial amount in GBP £');
    readln (initialAmount);
    endAmount := initialAmount * rate;
    writeln (endAmount);   
end.
This has been typed directly on the browser form a quick look around I
don't see any errors. If you have problems please post the error
reported and I"ll try to fix it.

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CyberFilth · 2015-04-01 20:20

You've nailed it! Thanks for that.

So the only issue was truncating the result withCode: [Select]:2:2 ?
So is that only used for outputting a number?

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taazz · 2015-04-01 21:37

Quote from: CyberFilth on April 01, 2015, 10:20:45 pmYou've nailed it!
Thanks for that.

So the only issue was truncating the result withCode: [Select]:2:2 ?
So is that only used for outputting a number?

yes the specific syntax is part of the writeln and not the compiler.