std::string causes link error

[jwhoag]

I'm attempting to use the std::string class, but I'm getting a linker error (writer.c.text._write_r+0x12): undefined reference to `_write'). I'm pretty sure this exact example worked in some previous Arduino/Teensyduino environment, but it's been quite a long time since I worked on my Teensy project and I've updated my installations since then. I'm using Ardiuno 1.8.16 and and Teensyduino 1.55. Teensy 3.1 is being targeted, although for kicks I also tried building for a 3.0 and 3.6 and got the same result. I also uninstalled Arduino/Teensy and re-installed. No luck.

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Here's the full minimized source code sketch that exhibits the issue:
Filename: Mini.ino
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#include <arduino.h>
#include <string>

void test(std::string& stdstr, const char* charstr)
{
stdstr = charstr;
}

void setup()
{
std::string output;
test(output, "hello");
}

void loop()
{
}

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Here's the error that is reported:
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Linking everything together...

"C:\\Program Files (x86)\\Arduino\\hardware\\teensy/../tools/arm/bin/arm-none-eabi-gcc" -O2 -Wl,--gc-sections,--relax,--defsym=__rtc_localtime=1633307146 "-TC:\\Program Files (x86)\\Arduino\\hardware\\teensy\\avr\\cores\\teensy3/mk20dx256.ld" -mthumb -mcpu=cortex-m4 -fsingle-precision-constant -o "c:\\proj\\Teensy31\\Builds/Mini.ino.elf" "c:\\proj\\Teensy31\\Builds\\sketch\\Mini.ino.cpp.o" "c:\\proj\\Teensy31\\Builds/..\\..\\..\\Users\\jwhoag\\AppData\\Local\\Temp\\arduino_cache_395686\\core\\core_teensy_avr_teensy31_usb_serial,speed_96,opt_o2std,keys_en-us_4939f5412a75a8560acb0f9e98268f02.a" "-Lc:\\proj\\Teensy31\\Builds" -larm_cortexM4l_math -lm -lstdc++

c:/program files (x86)/arduino/hardware/tools/arm/bin/../lib/gcc/arm-none-eabi/5.4.1/../../../../arm-none-eabi/lib/armv7e-m\libc.a(lib_a-writer.o): In function `_write_r':

writer.c.text._write_r+0x12): undefined reference to `_write'

collect2.exe: error: ld returned 1 exit status

Error compiling for board Teensy 3.2 / 3.1.

----------------------------------------------------------------
-Hardware: Teensy 3.1
-Wiring: not applicable to this question
-Software: nothing nonstandard. I only include <arduino.h> and <string>
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I searched the entire arduino directory structure and there's no file called writer.c, or any function called _write_r anywhere. I suspect this issue may be related to another post: https://forum.pjrc.com/threads/68342-std-deque-Won-t-Compile-for-Teensy-3-x.

What's also weird is that the following lines of code (which should essentially do the same thing) both link okay:

std::string stdstring("hello);
std::string stdstring = "hello";

I also changed the function test to use a pointer instead of a reference, and that still produces the same problem
i.e. --> void test(std::string* stdstr, const char* charstr)

I also changed the function test to use std::string::assign, and that still produces the same problem
i.e. --> stdstr.assign(charstr); instead of stdstr = charstr;

Any ideas? Thanks,
--Jeff

 

[thebigg]

Does this help you? https://forum.pjrc.com/threads/49802-STL-and-undefined-reference-to-std-__throw_bad_alloc()

 

[Simon.M]

Hi jwhoag,

here is a solution to the above code...



go to the tools menu and select optimise "smallest code" and compile, as you can see from the image it compiles ok

best regards

Simon.M

 

[jwhoag]

Ah interesting. The "smallest code" option causes it to work for me too.

I'd make a wild guess that maybe there's some debug code somewhere in the libraries that relies on _write_r (like printing some intermediate state), and it's not completely removed when the rest of the debug code is optimized out.

Thank you for the quick and accurate response Simon!

 

[Simon.M]

hi jwhoag,

your very welcome, it filled some time in my day and stopped me getting bored!

I did some digging around and looked at the build commands for each of the options, on the build commands used it's the -O option that seems to be the problem. I believe the -O is for optimisations. The smallest code uses -Os and the other options use -O1, -O2, -O3 and -Og for debug, all these fail on a teensy 3.x or teensy LC.

I see the "smallest code" as a set and forget option, the added bonus is it's the smallest code and you can squeeze more code in.

best regards

Simon.M