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Nickelgrass
Nickelgrass
Senior
December 7, 2022
Solved

I cannot overload a simple function in STM32CubeIDE with empty C++ project

  • December 7, 2022
  • 5 replies
  • 5145 views

Strange problem again.

I created a new empty STM32 project and selected C++. Now I made two functions

void test(uint8_t a)
{
 
}
 
void test(uint16_t a)
{
 
}

But I get an error of redefining the function test. The file (like all source files) has the ending .c and if I change it to .cpp then it works. But if I change any of my other source files to .cpp the functions in those files are not found any more. If I leave the ending .c then I cannot overload functions. What is going on here???

This topic has been closed for replies.
Best answer by TManiac

The STM HAL is written in plain C. And the main.c file will be in C too.

I don't know what the C++ switch on creation works :smirking_face: Maybe it comes from standard Eclipse window "create a new project". I was confused about it too.

You can write you own code in full C++ and call to it (in plain C style with the extern C linkage).

Do you have played with some STM tutorials/examples? They have a nice way to do it.

The picture shows my way (based on the STM idea). My "application", "Middleware" and "Driver" are written in C++.

The canInterface-"Driver" based on the plain C HAL.0693W00000WKXMDQA5.png

5 replies

TManiac
TManiac
Associate II
December 7, 2022

This is very basic.

STM32CubeIDE is based on gcc compiler.

*.c files will be compiled as plain C and *.cpp will be compiled with C++.

Overloading is a C++ thing and not allowed in plain C.

If you use C++ you must pay attention on the namespace of a function. Maybe you must deal with it over the header file where you publish you functions. But keep in mind you can't use the overloading inside a *.c file like the main.c.

TDK
TDK
Super User
December 8, 2022

If you want to use a C++ function (in a *.cpp file) within C, you need to define them with C linkage using extern "C".

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Nickelgrass
NickelgrassAuthor
Senior
December 8, 2022

Thanks for the replies. I know only c++ supports overloading. The point is that I created this project as a C++ project. So I expected all files to be .cpp in the first place. What difference does it then make if I create the project as C or C++ project? I would like everything to be C++.

TManiac
TManiacAnswer
Associate II
December 8, 2022

The STM HAL is written in plain C. And the main.c file will be in C too.

I don't know what the C++ switch on creation works :smirking_face: Maybe it comes from standard Eclipse window "create a new project". I was confused about it too.

You can write you own code in full C++ and call to it (in plain C style with the extern C linkage).

Do you have played with some STM tutorials/examples? They have a nice way to do it.

The picture shows my way (based on the STM idea). My "application", "Middleware" and "Driver" are written in C++.

The canInterface-"Driver" based on the plain C HAL.0693W00000WKXMDQA5.png

Nickelgrass
NickelgrassAuthor
Senior
December 8, 2022

Thank you for the detailed answer. I still get the "redefined" error for the functions in some files. Strangeley in some it does work (?). I have not idea what is going on. I never had this strange behaviour any where else. I guess I will just stick to c for now.

TManiac
TManiac
Associate II
December 8, 2022

You must not use overloading (or other C++ specific things inside the headers that you include to a plain C file.

If you want to use only one header file there must be a wrapper function and excludion of the C++ stuff

For example this header should work:

#ifndef __inclusion_protection__
#define inclusion_protection
 
#ifdef __cplusplus
extern "C" {
#endif
 
/* one function is ok.
Maybe this one it handles the bigest value */
void test(uint16_t a);
 
#ifdef __cplusplus
}
#endif
 
/* all coming up will be ignored in plain C */
#ifdef __cplusplus
 
/* this is a C++ function */
void test(uint8_t a); 
 
#ifdef __cplusplus
 
#endif /* inclusion_protection */

Nickelgrass
NickelgrassAuthor
Senior
December 22, 2022

Thank you for the explanation.

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