Using Freepascal\Lazarus JSON Libraries
- by Gizmo_the_Great
I'm hoping for a bit of a "simpletons" demo\explanation for using Lazarus\Freepascal JSON parsing. I've asked a question here but all the replies are "read this" and none of them are really helping me get a grasp because the examples are bit too in-depth and I'm seeking a very simple example to help me understand how it works.
In brief, my program reads an untyped binary file in chunks of 4096 bytes. The raw data then gets converted to ASCII and stored in a string. It then goes through the variable looking for certain patterns, which, it turned out, are JSON data structures. I've currently coded the parsing the hard way using Pos and ExtractANSIString etc. But I'vesince learnt that there are JSON libraries for Lazarus & FPC, namely fcl-json, fpjson, jsonparser, jsonscanner etc.
https://bitbucket.org/reiniero/fpctwit/src
http://fossies.org/unix/misc/fpcbuild-2.6.0.tar.gz:a/fpcbuild-2.6.0/fpcsrc/packages/fcl-json/src/
http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/packages/fcl-json/examples/
However, I still can't quite work out HOW I read my string variable and parse it for JSON data and then access those JSON structures.
Can anyone give me a very simple example, to help getting me going?
My code so far (without JSON) is something like this:
try
SourceFile.Position := 0;
while TotalBytesRead < SourceFile.Size do
begin
BytesRead := SourceFile.Read(Buffer,sizeof(Buffer));
inc(TotalBytesRead, BytesRead);
StringContent := StripNonAsciiExceptCRLF(Buffer); // A custom function to strip out binary garbage leaving just ASCII readable text
if Pos('MySearchValue', StringContent) > 0 then
begin
// Do the parsing. This is where I need to do the JSON stuff
...
