Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: ESP-12
• Core Version: 3.0.2
• Development Env: Arduino IDE 1.8.15
• Operating System: Ubuntu (Linux Mint)

Settings in IDE

• Module: "Nodemcu 1.0 (ESP-12 Module)"
• Flash Mode: ?? [qio|dio|other]
• Flash Size: 4MB
• lwip Variant: v2 Lower Memory
• Reset Method: ?? [ck|nodemcu]
• Flash Frequency: ?? [40Mhz]
• CPU Frequency: 80Mhz
• Upload Using: SERIAL
• Upload Speed: 115200 (serial upload only)

Problem Description

When StreamString.h is included from the *.cpp file and <algorithm> is not included before, following error message is given by the compiler:

error: 'min' is not a member of 'std'

In file included from /home/testuser/git/StreamStringBugExample/Test1.cpp:4:
/home/testuser/.arduino15/packages/esp8266/hardware/esp8266/3.0.2/cores/esp8266/StreamString.h: In member function 'virtual int S2Stream::read(uint8_t*, size_t)':
/home/testuser/.arduino15/packages/esp8266/hardware/esp8266/3.0.2/cores/esp8266/StreamString.h:89:29: error: 'min' is not a member of 'std'
   89 |             size_t l = std::min(len, (size_t)string->length());
      |                             ^~~

The problem does not appear if StreamString.h is included from the *.ino file.

MCVE Sketch (two files)

StreamStringBugExample.ino

void do_test();

void setup() {
  do_test();
}

void loop() {
}

Test1.cpp

// #include <WString.h> // not needed as it is included from StreamString.h
#include <Stream.h> // this include is also needed for the StreamString.h
// #include <algorithm> // with this not commented out, the code would compile
#include <StreamString.h>

void do_test()
{
  StreamString s;
  s.println("This is a test");
}

Possible solution

At the beginning of StreamString.h, one should include the headers that are used by this file:

#include "Stream.h"
#include <algorithm>