STL support.

[jfjlaros]

Continuation of #23.

[gpantazis]

Ok so due to the nature of the job, I can't share my actual code using std::string.

Instead I have attached a minimal project, as well as the edits to each of the necessary files.

Minimal Project

test)stl_str.ino:

#include <string>

#include "simpleRPC.h"

void setup() {
    Serial.begin(9600);
    while(!Serial) {}
}

std::string greet(std::string person)
{
    return "Hello, "  + person + "\n";
}

void loop() {
    interface(Serial,
              greet, "greet:");
}

Modified Files

Modified files are below. Note that the changes in all of them mirror the functions for String, the Arduino built-in std::string equivalent. For std::vector and std::array you would likely follow the definitions for Vector

types.tcc:

#include <string>
....

/*! \ingroup types
 * \copydoc rpcTypeOf(Stream&, bool) */
inline void rpcTypeOf(Stream& io, std::string&) {
  rpcPrint(io, "s");
}

write.tcc

#include <string>
...
/*! \ingroup write
 * \copydoc rpcWrite(Stream&, T*) */
inline void rpcWrite(Stream& io, std::string* data) {
  rpcPrint(io, *data, '\0');
}

print.tcc:

#include <string>
...
/*! \ingroup print
 * \copydoc rpcPrint(Stream&, T) */
inline void rpcPrint(Stream& io, std::string& data) {
  rpcPrint(io, data.c_str());
}

read.tcc:

#include <string>
...
/*! \ingroup read
 * \copydoc rpcRead(Stream&, T*) */
inline void rpcRead(Stream& io, std::string* data) {
  char character;

  rpcRead(io, &character);

  while (character) {
    *data += character;
    rpcRead(io, &character);
  }
}

Build Instructions

This is where for non-Teensy boards I am not too clear on. I checked through the base Arduino avr folder and there are no C++ libraries. Downloading support for the arm boards (Arduino Due) seems to yield C++ libs as part of their ARM compiler , but not -lstdc++_nano. This may be because they use an older version of gcc (4.8.3-2014q1). That said -lstdc++ is available. This coupled with -specs=nano.specs should have the same effect (on code size) as -lstdc++_nano.

So I got the code above to compile for Arduino Due by editing this file, C:\Users\<USER>\Local\ArduinoXX\Packages\arduino\hardware\sam\1.6.12\platform.txt, and appending -lstdc++ and -specs=nano.specs to the end of this line (see code block below). I don't know how to do this using arduino-cli, boards.txt or platform.local.txt

...
## Combine gc-sections, archives, and objects
recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" -mcpu={build.mcu} -mthumb {compiler.c.elf.flags} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--entry=Reset_Handler -Wl,--unresolved-symbols=report-all -Wl,--warn-common -Wl,--warn-section-align -Wl,--start-group {compiler.combine.flags} {object_files} "{build.variant.path}/{build.variant_system_lib}" "{build.path}/{archive_file}" -Wl,--end-group -lm -lgcc -lstdc++ -specs=nano.specs
...

Note that adding -specs=nano.specs to the end of the line above drastically reduces the size of the resulting sketch from 74592 bytes to 12488 bytes (!).

[jfjlaros]

I managed to compile your sketch using arduino-cli. Below are my notes.

Installation

Install the core for ARM boards.

arduino-cli core install arduino:sam

Edit ~/arduino15/packages/arduino/hardware/sam/1.6.12/platform.txt, add -lstdc++ -specs=nano.specs to the end of the recipe.c.combine.pattern line.

Example sketch

Configure the sketch for the right core.

arduino-cli board attach arduino:sam:arduino_due_x

Content of stl.ino:

#include "stl.h"


std::string greet(std::string person) {
  return "Hello, " + person + "\n";
}


void setup() {
  Serial.begin(9600);
}

void loop() {
  interface(Serial, greet, "");
}

Content of stl.h:

#include <string>

#include <simpleRPC.h>


inline void rpcTypeOf(Stream& io, std::string&) {
  rpcPrint(io, "s");
}

inline void rpcWrite(Stream& io, std::string* data) {
  rpcPrint(io, *data, '\0');
}

inline void rpcPrint(Stream& io, std::string& data) {
  rpcPrint(io, data.c_str());
}

inline void rpcRead(Stream& io, std::string* data) {
  char character;

  rpcRead(io, &character);

  while (character) {
    *data += character;
    rpcRead(io, &character);
  }
}

Compilation

Compile the sketch.

arduino-cli compile

[jfjlaros]

To use the STL data types, we could offer an excerpt of the notes above as well as an alternative include line, e.g.,

#include <simpleRPC_STL.h>

That way we would have support for both the custom data types as well as the ones in the STL.

[jfjlaros]

The Arduino library now has experimental STL support. I have no idea whether it works since I have no way of testing it.

You can find the example sketch here.

(edit)

Apparently the ESP32 core has STL support out of the box, so I can do some testing after all. In this sketch std::string and std::vector seem to be working.