string help

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Joe31093

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I have a simple test program that uses two strings. But when I include the second string (world), the program fails to link. Can someone help me understand the issue? Thanks. Teensyduino, Version 1.39, Arduino 1.8.4.

Code: 
#include <string>

using namespace std;

void setup() {
  // put your setup code here, to run once:
  Serial1.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
  
  string hello("hello");
  Serial1.println(hello.c_str());

  string world("world");
  Serial1.println(world.c_str());

  delay(1000);
}

/Applications/Arduino.app/Contents/Java/arduino-builder -dump-prefs -logger=machine -hardware /Applications/Arduino.app/Contents/Java/hardware -tools /Applications/Arduino.app/Contents/Java/tools-builder -tools /Applications/Arduino.app/Contents/Java/hardware/tools/avr -built-in-libraries /Applications/Arduino.app/Contents/Java/libraries -libraries /Users/jli1/Documents/Arduino/libraries -fqbn=teensy:avr:teensy36:usb=serial,speed=180,opt=o2std,keys=en-us -ide-version=10804 -build-path /var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581 -warnings=all -build-cache /var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_cache_873730 -verbose /Users/jli1/Documents/Arduino/sketch_oct09a/sketch_oct09a.ino
/Applications/Arduino.app/Contents/Java/arduino-builder -compile -logger=machine -hardware /Applications/Arduino.app/Contents/Java/hardware -tools /Applications/Arduino.app/Contents/Java/tools-builder -tools /Applications/Arduino.app/Contents/Java/hardware/tools/avr -built-in-libraries /Applications/Arduino.app/Contents/Java/libraries -libraries /Users/jli1/Documents/Arduino/libraries -fqbn=teensy:avr:teensy36:usb=serial,speed=180,opt=o2std,keys=en-us -ide-version=10804 -build-path /var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581 -warnings=all -build-cache /var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_cache_873730 -verbose /Users/jli1/Documents/Arduino/sketch_oct09a/sketch_oct09a.ino
Using board 'teensy36' from platform in folder: /Applications/Arduino.app/Contents/Java/hardware/teensy/avr
Using core 'teensy3' from platform in folder: /Applications/Arduino.app/Contents/Java/hardware/teensy/avr
Detecting libraries used...
"/Applications/Arduino.app/Contents/Java/hardware/teensy/../tools/arm/bin/arm-none-eabi-g++" -E -CC -x c++ -w -g -Wall -ffunction-sections -fdata-sections -nostdlib -fno-exceptions -felide-constructors -std=gnu++14 -fno-rtti -mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -D__MK66FX1M0__ -DTEENSYDUINO=139 -DARDUINO=10804 -DF_CPU=180000000 -DUSB_SERIAL -DLAYOUT_US_ENGLISH "-I/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/cores/teensy3" "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch/sketch_oct09a.ino.cpp" -o "/dev/null"
Generating function prototypes...
"/Applications/Arduino.app/Contents/Java/hardware/teensy/../tools/arm/bin/arm-none-eabi-g++" -E -CC -x c++ -w -g -Wall -ffunction-sections -fdata-sections -nostdlib -fno-exceptions -felide-constructors -std=gnu++14 -fno-rtti -mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -D__MK66FX1M0__ -DTEENSYDUINO=139 -DARDUINO=10804 -DF_CPU=180000000 -DUSB_SERIAL -DLAYOUT_US_ENGLISH "-I/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/cores/teensy3" "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch/sketch_oct09a.ino.cpp" -o "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/preproc/ctags_target_for_gcc_minus_e.cpp"
"/Applications/Arduino.app/Contents/Java/tools-builder/ctags/5.8-arduino11/ctags" -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/preproc/ctags_target_for_gcc_minus_e.cpp"
Compiling sketch...
"/Applications/Arduino.app/Contents/Java/hardware/teensy/../tools/arm/bin/arm-none-eabi-g++" -c -O2 -g -Wall -ffunction-sections -fdata-sections -nostdlib -MMD -fno-exceptions -felide-constructors -std=gnu++14 -fno-rtti -mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -D__MK66FX1M0__ -DTEENSYDUINO=139 -DARDUINO=10804 -DF_CPU=180000000 -DUSB_SERIAL -DLAYOUT_US_ENGLISH "-I/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/cores/teensy3" "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch/sketch_oct09a.ino.cpp" -o "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch/sketch_oct09a.ino.cpp.o"
Compiling libraries...
Compiling core...
Using precompiled core
Linking everything together...
"/Applications/Arduino.app/Contents/Java/hardware/teensy/../tools/arm/bin/arm-none-eabi-gcc" -O2 -Wl,--gc-sections,--relax,--defsym=__rtc_localtime=1507558569 "-T/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/cores/teensy3/mk66fx1m0.ld" -lstdc++ -mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -o "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch_oct09a.ino.elf" "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch/sketch_oct09a.ino.cpp.o" "/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/../arduino_cache_873730/core/core_teensy_avr_teensy36_usb_serial,speed_180,opt_o2std,keys_en-us_cee3a1d70ca5f7f18ab44a012a95ee10.a" "-L/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581" -larm_cortexM4lf_math -lm
/var/folders/q4/djp0qrzs55x04tt5rt_qhpsw0000gp/T/arduino_build_273581/sketch/sketch_oct09a.ino.cpp.o: In function `void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char const*>(char const*, char const*, std::forward_iterator_tag)':
/Applications/Arduino.app/Contents/Java/hardware/tools/arm/arm-none-eabi/include/c++/5.4.1/bits/basic_string.tcc:219: undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_create(unsigned int&, unsigned int)'
/Applications/Arduino.app/Contents/Java/hardware/tools/arm/arm-none-eabi/include/c++/5.4.1/bits/basic_string.tcc:212: undefined reference to `std::__throw_logic_error(char const*)'
collect2: error: ld returned 1 exit status
Error compiling for board Teensy 3.6.
 
"String" is not part of the namespace std. I was able to use std::string in 1.35, just trying to understand what I need to do with the latest update.
 
Teensyduino, as Arduino, uses String class for representing string objects:
https://www.arduino.cc/en/Reference/StringObject

You can see the String class header in the String.h. I am working on Mac, this file is:
/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/cores/teensy/WString.h

I think that stdlib C++ string is not supported any more.


Try this:
Code: 
void setup() {
  // put your setup code here, to run once:
  Serial1.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
  
  String hello("hello");
  Serial1.println(hello);

  String world("world");
  Serial1.println(world);

  delay(1000);
}
 
As noted string doesn't exist from the code above - but String does as this example works without the commented items.

Not sure what the heap effect is of the loop() local String's? Or what features might be excluded with the default String that is included?

Code: 
//#include <string>
//using namespace std;

void setup() {
  Serial.begin(115200);
}

void loop() {
  String hello("hello ");
  Serial.print(hello.c_str());
  String world("world @");
  world += millis();
  Serial.println(world.c_str());
  delay(1000);
}

sample output:
...
hello world @261408
hello world @262409
...
Click to expand...
 
String allocates memory on the heap, and implicitly called destructor releases memory.

You can get free memory size with this function:
Code: 
// https://forum.pjrc.com/threads/23256-Get-Free-Memory-for-Teensy-3-0

extern "C" char* sbrk(int incr);

static size_t freeRAM (void) {
  int top; // For getting stack address
  return ((size_t) &top) - ((size_t) sbrk(0)) ;
}

And display the returned value with:
Code: 
void loop() {
  ...
  Serial.print("Free Ram: ");
  Serial.println(freeRAM());
  ...
}
 
That was a somewhat rhetorical question - just wondering if those local's would behave well on the heap - and noting that heap usage can do odd things when it fragments.

It seems they do behave okay and don't - as used - cause any fragmentation with loop() local 'repeat' creation.

I added the FreeRam() code and making them global (on T_3.2) does result in them having more Free Ram to a small degree where Free is 57308 when global and 57276 when as shown below versus above as local vars.

Code: 
String hello("hello ");
String world("world @");

void loop() {
  Serial.print(hello.c_str());
  world = "world ";
  world += millis();
  // ...
 
Joe31093 said:
Can you explain? Am I not able to use std::string?
Click to expand...

To more directly answer your question, Teensy generally follows the Arduino conventions and aims for Arduino compatibility.

Arduino has very limited support for the C++ standard library functions. You can expect most C++ std namespace stuff to not work.
 
Thanks for the help everyone. Was there something specific that was changed to make std::string not work from 1.35 to 1.39?
 
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