'template with C linkage' error when using template keyword in main.cpp

Question

In my main.cpp, I create multiple objects of self-defined classes, e.g.:

#include "device_manager.hpp"
DeviceManager deviceManager; //compiles and works just fine

However, when I try to implement a simple template just below in the same main.cpp:

template <typename T>
inline T max(T a, T b) {
    return a > b ? a : b;
}

I get:

template with C linkage main.cpp line 35    C/C++ Problem

Seems like the compiler fails to understand the template keyword. I did not add any extern "C" blocks inside my main.cpp. I have tried using gnu++14 compiler (C++14 + gnu extensions) and gnu++11 for compiling my C++ code and gnu11 for compiling C code inside my C-to-C++ converted project. What could possibly go wrong with understanding the template keyword?

EDIT: The project was generated as a C project which I later converted to a C++ project using an IDE tool, also changing main.c to main.cpp. Since then, I could declare my class objects in main.cpp without problems, but when I try to use the template keyword in main.cpp, I get the aforementioned error as though it was inside extern "C" statement (but I didn't put it there).

C compiler command: arm-atollic-eabi-gcc -c, compiler: gnu11

C++ compiler command: arm-atollic-eabi-g++ -c, compiler: gnu++14

Linker command: arm-atollic-eabi-g++ (I am on an ARM embedded system, writing in Atollic TrueStudio IDE)

@jwdonahue The question mentions that both C code and C++ are compiled, and apparently the problem is that linker/compiler handles C++ as C. Are you sure about the tag being extraneous? — Zeta
– Zeta, Commented May 10, 2020 at 19:49
Please edit your question to provide a minimal reproducible example. You might also want to show how you compile/link. — G.M.
– G.M., Commented May 10, 2020 at 19:49
Question already edited. I will be happy to answer more detailed questions on my problem — Slighten
– Slighten, Commented May 10, 2020 at 20:00

Alexey Polyudov · Accepted Answer · 2020-05-10 19:52:33Z

3

the "C linkage" part makes me suspect that you might not close the

extern "C" {
//...
}

declaration in your header file.

this is the error exactly the code like this will produce:

extern "C" {
template <typename T>
inline T max(T a, T b) {
  return a > b ? a : b;
}
}

answered May 10, 2020 at 19:52

Alexey Polyudov

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4 Comments

Slighten Over a year ago

I am aware of that, but as I wrote, checked all possible extern "C" blocks and this is not the case. Still, declaring classes objects just a line above in main.cpp works fine for me

Alexey Polyudov Over a year ago

please, do me a favor, and remove that header; if template compiles OK without it, there MUST be something you missed inside that header (or transitively in any header it includes).

Slighten Over a year ago

That might be a case with an extern "C" lost somewhere in files included from main.h, just began tracking it

Slighten Over a year ago

That apparently solved the issue. There was a block of extern "C" { not closed with a } in a library (yes) included file. Beware of your included libraries

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