Trying to track down a bug when i wanted to see how much ram i had left. I created a variable uint8_t my_data[256]; I then started kicking it up to see when the compiler would fail as it would run out of ram. I changed it from 256, 512,1024,2048… and so on, it kept compiling. Then i just slapped…

At first locally. Then i jumped to the web IDE and tried it there as well. In both cases it passed. If you take your uint8_t testarray[6444]; and change it to uint8_t testarray[6444000]; It then fails. which it should. However if you then move it inside the setup() function it passes. Something …

Could this come from the fact that automatic variables are not actually reserved at compile time, but only “created” on call of the procedure by pushing them onto the stack? They only live as long the called function lives and get popped off during function-return-cleanup-action. This way you’d ge…

@ScruffR is right. The compiler does not know what will happen to automatic variables. I do get a warning that I am not using the var when building locally: ../src/application.cpp: In function 'void loop()': ../src/application.cpp:15:11: warning: unused variable 'testarray' [-Wunused-variable] …

Using the web IDE I just tried this and it still compiles. void setup() { uint8_t testarray[644400]; testarray[0] = 0; }

Sure it will compile, since this is not a problem the compiler does check for. As said above these variables are sort of non-existent before runtime but the compiler only cares about things that exist at compile time - which automatic variables don’t. It’s just like setting a pointer address outsi…

Try this to check your free RAM in app: [image] How to know how much RAM/Flash i am using Cloud I’ve been wanting to do this, so thanks for the push! Read the comments near the bottom… seem legit? Adapted from: http://playgr…

@BDub this is a nice way to figure out mem usage at runtime :wink: But this seems to be the pivotal point: Runtime mem usage is not anything the compiler could reliably care about. This will always be the developers duty - e.g. estimate stack and heap demand in different use cases.

[image] ScruffR: Sure it will compile, since this is not a problem the compiler does check for. As said above these variables are sort of non-existent before runtime but the compiler only cares about things that exist at compile time - which automatic variables don't.It's just like setting a po…

@seulater having the array declared global or automatic is nothing alike. So it’s not the same array anymore. When declaring it global you tell the compiler to reserve some space for that array and provide a pointer to this space for referencing it. When declaring it automatic you just tell the c…

@ScruffR , Thanks for the explanation. Yet it does not make sense to me that it should do this. Lets say for conversation sake that i am using a processor with 8k of ram. I create a global array using almost all of the ram. char buf[8100]; Then i have a function and in there i also create anothe…

uint8_t my_data[256000]; Compiles?

Troubleshooting

BDub March 8, 2014, 3:36pm 8

Try this to check your free RAM in app:

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uint8_t my_data[256000]; Compiles?

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