question

Choi Hyun Woong asked Jul 16, '24 Jason Lightfoot commented Jul 16, '24

How do I convert a json type message to a string?

As always, thank you for your help.

How do I convert a json type message to a string?

For example, if you try to convert the following json message to a string:

{"type":"A","pose":{"x":0,"y":0,"theta":0}}

string str = "{"type":"A","pose":{"x":0,"y":0,"theta":0}}";

The following error occurs:

Flexscript Error VIEW:/active/MainPanel/BackPanel/SplitterXPane/SplitterYPane/SplitterXPane~2/ToolTabPane/TabControl/ScriptConsole/Script>script Line 1 syntax error

Could not finish parsing because of previous errors.

What's the problem?

Software Version:

FlexSim 24.1.0

json data

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Joerg Vogel answered Jul 16, '24 Jason Lightfoot commented Jul 16, '24

If you would use a map by keywords type and pose, then you could build a string by stringify method, won’t you?

Edit: The problem is, that you need to parse a double quotation mark by an escape sequence into a string. Otherwise you would close a string.

\'	Inserts a single quotation mark in the string.

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Jason Lightfoot ♦♦ commented · Jul 16 at 10:08 AM

So:

string s="{\"type\":\"A\",\"pose\":{\"x\":0,\"y\":0,\"theta\":0}}";
return JSON.parse(s);

returns:

Map:    {type: A, pose: {x: 0, y: 0, theta: 0}}

Of course if you're receiving a message from elsewhere then you don't need to convert anything or use escape characters - it's just when you're constructing it in FlexSim using this technique.

As Jörg points out you can use a map and then stringify it for your test:

Map m;
m.type="A";
Map p;
p.x=0;
p.y=0;
p.theta=0;
m.pose=p;
return JSON.stringify(m);

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Choi Hyun Woong Jason Lightfoot ♦♦ commented · Jul 16 at 03:11 PM

Thank you for your kindly reply!

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Choi Hyun Woong commented · Jul 16 at 03:10 PM

Thank you for reply!

Are JSON messages received through MQTT broker stored as strings in emulation variables(Emulation().variables) without double quotation? Or is double quotation applied internally and stored as a string?

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Jason Lightfoot ♦♦ Choi Hyun Woong commented · Jul 16 at 03:33 PM

Messages should have double quotation marks in the string - the need for escape characters is just to tell the FlexScript interpreter which quotes are included in the string and which denote the start/end of the string.

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