int main()
{
for(int i=0; i<=100; i+=20) {
fprintf(stdout, "%d\n", i);
fflush(stdout);
usleep(500000);
}
return(0);
}
```
---
### Author:  [@Colin](https://discourse.nodered.org/u/Colin)
#### Post date: [5 October 2025 16:34 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/2 "2025-10-05T16:34:35Z")
Add debug nodes to all outputs of the exec node, set them to Output Complete Message and check all properties of the outputs. There will probably be a helpful error message there.
Have you specified the full path to the executable file?
I don't see the flow in your repository.
---
### Author:  [@hardillb](https://discourse.nodered.org/u/hardillb)
#### Post date: [5 October 2025 16:35 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/3 "2025-10-05T16:35:18Z")
You've not checked in the flow file so we have no idea how you've configured the exec node.
Also you probably want to swap the dashboard start button for a inject node to get started and set the debug node to whole message not just payload to see more.
You should also check the Node-RED logs for more error messages.
As it is there isn't really anything we can help with so far.
And I assume you have tested running the compiles c program from the command line first?
The code when complied and run with a full path works just fine on my Ubuntu box with NR 4.1.0
---
### Author:  [@jbudd](https://discourse.nodered.org/u/jbudd)
#### Post date: [5 October 2025 17:09 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/4 "2025-10-05T17:09:05Z")
~~Please don't be offended by the question, but your exec node is trying to run the compiled executable, not the C source code?~~ Edit: I think that would give rc -13
Does it make a difference if you specify the full pathname of the executable eg `/home/pedro/.node-red/bin/gen_percent` (or wherever the file is)?
One cause of rc -2 is that the OS cannot find the file to execute it.
---
### Author:  [@pedro\_uno](https://discourse.nodered.org/u/pedro_uno)
#### Post date: [6 October 2025 12:58 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/5 "2025-10-06T12:58:57Z")
The flow is checked in here, [node-red\_experiments/c2progress/.node-red at main · hdlguy/node-red\_experiments · GitHub](https://github.com/hdlguy/node-red_experiments/tree/main/c2progress/.node-red), but it is a hidden folder so sometimes I also miss seeing it.
I will try the an inject node but I actually want have the code started by a user hitting a button. I think I have tried several forms of the path. I will try to hard code the full path again. That should be ok since the application is an embedded system. I don't really need relative path names.
I will also change the debug node to whole messages.
I was about to give up on this but since you guys are so helpful, I will keep trying.
---
### Author:  [@hardillb](https://discourse.nodered.org/u/hardillb)
#### Post date: [6 October 2025 13:34 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/6 "2025-10-06T13:34:31Z")
The flow is not in that directory
---
### Author:  [@jbudd](https://discourse.nodered.org/u/jbudd)
#### Post date: [6 October 2025 14:00 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/7 "2025-10-06T14:00:27Z")
> [@hardillb](#):
>
> The flow is not in that directory
The code which @pedro_uno included in his original post is at [https://github.com/hdlguy/node-red\_experiments/blob/main/c2progress/c\_code/gen\_percent.c](https://github.com/hdlguy/node-red_experiments/blob/main/c2progress/c_code/gen_percent.c)
---
### Author:  [@hardillb](https://discourse.nodered.org/u/hardillb)
#### Post date: [6 October 2025 14:12 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/8 "2025-10-06T14:12:14Z")
@jbudd I'm not interested in the C code, I have that, I want to see the Node-RED flow so I can actually see how the exec node is configured (e.g. is the full path to the executable provided)
---
### Author:  [@pedro\_uno](https://discourse.nodered.org/u/pedro_uno)
#### Post date: [6 October 2025 14:35 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/9 "2025-10-06T14:35:25Z")
OK, thanks again for the attention to my problem. I have now committed flows.json to the repo. I also got the got the flow to run with the exec node in spawn mode. The trick was to use an absolute path to the compiled C command.
My purpose was to use the exec code in spawn mode so that it could drive a progress bar during flash memory programming stages. In addition to the absolute path, I needed to put a fflush(stdout) command after each printf of the C code. I also needed to use a change block to convert the string to a number. All these changes were the result of suggestions on this forum.
Thanks for all the support and thanks for node-red itself. I do embedded design involving FPGAs and I need a way to create web UIs without being a web developer. Node-Red is really working out for me.
---
### Author:  [@pedro\_uno](https://discourse.nodered.org/u/pedro_uno)
#### Post date: [9 October 2025 14:01 UTC](https://discourse.nodered.org/t/how-to-spawn-c-code-using-exec/99273/10 "2025-10-09T14:01:17Z")
I uploaded a video of the DB1 chart node displaying a rapidly updating waveform. It is 600KB but it shows what is possible.
```auto
https://github.com/hdlguy/node-red_experiments/blob/main/db2_chart/db1_waveform_performance.webm
```