Including library take ram and storage?

Projects Programming
1

Hi,

I want to make a library that not take any storage and ram. And i'm doing a simple research at the arduino ide.

If we make a new file in the IDE and compile it, compiler return :

Sketch uses 444 bytes (1%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.

if we include a library like newping , compiler return same as not include anything :

Sketch uses 444 bytes (1%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.

if we include ir remote library, returns :

Sketch uses 968 bytes (3%) of program storage space. Maximum is 32256 bytes.
Global variables use 167 bytes (8%) of dynamic memory, leaving 1881 bytes for local variables. Maximum is 2048 bytes.

Then i check the library not much different in the header (or i don't know). I want to know what's the different about including library and the structure (maybe?) in the library affect ram and storage?

Thanks!

2

Can you show the test sketches you used?

3

If your library simply defines a class, then including it, without creating an instance of the class, then no additional SRAM or FLASH memory is used.

If your library defines a bunch of global variables, then including it will cause all the global variables to be created, using SRAM but no FLASH memory.

If your library defines a class AND creates a global instance of the class, then SRAM and FLASH will be used.

Your goal of creating a library that uses no FLASH and no SRAM is completely unrealistic unless your library does nothing.

4

robtillaart:
Can you show the test sketches you used?

Blank:

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

ir remote:

#include <IRremote.h>
void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

NewPing :

#include <NewPing.h>
void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

PaulS:
If your library simply defines a class, then including it, without creating an instance of the class, then no additional SRAM or FLASH memory is used.

If your library defines a bunch of global variables, then including it will cause all the global variables to be created, using SRAM but no FLASH memory.

If your library defines a class AND creates a global instance of the class, then SRAM and FLASH will be used.

Your goal of creating a library that uses no FLASH and no SRAM is completely unrealistic unless your library does nothing.

i missed something i don't mean to make library without no flash and sram but just like your first point.

Okay Understood! Thanks!

5

+1 for PaulS' explanation

Besides the compile time SRAM usage, more important is the runtime RAM usage.
Especially "When heap meets stack" (could be the title of a tech poem).

The function below checks the free RAM by creating a variable and calculate its position relative to some internal thingy.

int freeRam () {
    extern int __heap_start, *__brkval; 
    int v; 
    return (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval); 
};