How to parse JSON array in RAd Studio?
I am trying to parse the following Json document:
[
{"EventType":49,"Code":"234","EventDate":"20050202", "Result":1},
{"EventType":48,"Code":"0120","EventDate":"20130201", "Group":"g1"}
]
I am using the following code:
TJSONObject* jsonread0 = (TJSONObject*) TJSONObject::ParseJSONValue(TEncoding::ASCII->GetBytes(Memo1->Lines->Text), 0);
for(int i=0;i<jsonread0->Size();i++)
{
TJSONPair* pair = jsonread0->Get(i);
It pair.JsonValue
is NULL at this point . What do I need to do to read the values?
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You are not producing the correct JSON String, you have to use it as a TJSONArray and then iterate over the elements.
try these samples
Delphi
{$APPTYPE CONSOLE}
uses
DBXJSON,
System.SysUtils;
Const
StrJson =
'['+
'{"EventType":49,"Code":"234","EventDate":"20050202", "Result":1},'+
'{"EventType":48,"Code":"0120","EventDate":"20130201", "Group":"g1"}'+
']';
procedure ParseJson;
var
LJsonArr : TJSONArray;
LJsonValue : TJSONValue;
LItem : TJSONValue;
begin
LJsonArr := TJSONObject.ParseJSONValue(TEncoding.ASCII.GetBytes(StrJson),0) as TJSONArray;
for LJsonValue in LJsonArr do
begin
for LItem in TJSONArray(LJsonValue) do
Writeln(Format('%s : %s',[TJSONPair(LItem).JsonString.Value, TJSONPair(LItem).JsonValue.Value]));
Writeln;
end;
end;
begin
try
ParseJson;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
Readln;
end.
C ++ Builder
#include <vcl.h>
#include <windows.h>
#pragma hdrstop
#pragma argsused
#include <tchar.h>
#include <stdio.h>
#include <DBXJSON.hpp>
#include <iostream>
int _tmain(int argc, _TCHAR* argv[])
{
TJSONArray* LJsonArr = (TJSONArray*)TJSONObject::ParseJSONValue(
BytesOf((UnicodeString)"[{\"EventType\":49,\"Code\":\"234\",\"EventDate\":\"20050202\", \"Result\":1}, {\"EventType\":48,\"Code\":\"0120\",\"EventDate\":\"20130201\", \"Group\":\"g1\"}]"),0);
int size = LJsonArr->Size();
for (int i = 0; i < size; ++i)
{
TJSONValue* LJsonValue = LJsonArr->Get(i);
TJSONArray* LJsonArr2 = (TJSONArray*)LJsonValue;
int size2 = LJsonArr2->Size();
for (int j = 0; j < size2; ++j)
{
TJSONValue* LItem = LJsonArr2->Get(j);
TJSONPair* LPair = (TJSONPair*)LItem;
printf("%s %s \n", (UTF8String )(LPair->JsonString->Value()).c_str(), (UTF8String )(LPair->JsonValue->Value()).c_str());
}
}
std::cin.get();
return 0;
}
This will return
EventType : 49
Code : 234
EventDate : 20050202
Result : 1
EventType : 48
Code : 0120
EventDate : 20130201
Group : g1
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dbExpress JSON parser was considered cumbersome and sometimes problematic.
Maybe you can choose a number of third party parsers, for example this shows the read array: http://code.google.com/p/superobject/wiki/first_steps
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You have an invalid type, so you see undefined behavior. A null result is just one of many possible results that you might expect from this code. The function ParseJSONValue
in this case should return TJsonArray
, not TJsonObject
. Although both classes have methods Get
, they are not interchangeable.
The array method Get
returns a TJsonValue
, not TJsonPair
. For this specific data, you can enter a value TJsonObject
because your data is an array of two objects.
Use dynamic_cast
or Delphi as
to port from one class to another.
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you can get array from JSON string also using JSonCBuilderBlog library for C ++ Builder (free and open source):
UnicodeString JSONSource =
"[{\"EventType\":49,\"Code\":\"234\",\"EventDate\":\"20050202\", \"Result\":1},"
"{\"EventType\":48,\"Code\":\"0120\",\"EventDate\":\"20130201\",\"Group\":\"g1\"}]";
int Type;
UnicodeString Code;
UnicodeString Date;
int Result;
TMetaObject MyArray;
MyArray.Decode(JSONSource);
for(int i=0; i < MyArray.Count(); i++)
{
Type = MyArray[i]["EventType"];
Code = MyArray[i]["Code"];
Date = MyArray[i]["EventDate"];
}
The syntax is very simple, see the following link for reference: JSONCBuilderBlog library.
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