Detect #define from another library or header include of another library in my library

Libraries
1

Hello,

Basically as title says, I’m developing library that needs to define something if another library is present.

I have tried:

#if __has_include("avr8-stub.h")
#define AVR_DEBUG
#endif

#if defined(__has_include)
#warning "__has_include is supported by your compiler."
#else
#warning "__has_include is not supported by your compiler."
#endif

#if defined(AVR_DEBUG)
#warning "Debug mode enabled." // this is hilighted
#else
#warning "Debug mode disabled."
#endif

VSCode ide sees it, compiler does not.

warning: #warning "__has_include is supported by your compiler." [-Wcpp]
 #warning "__has_include is supported by your compiler."

warning: #warning "Debug mode disabled." [-Wcpp]
 #warning "Debug mode disabled."
  ^~~~~~~

Do you have any suggestions how to implement this in my library without any additional configuration from the user using the library. I know that this can be easly fixed with simple -DAVR_DEBUG in platformio.ini but i would like to make this automated without the need for any manual intervention with defining or custom scripts.

I have avr8-stub.h included in main.cpp before my library but my library gets compiled for itself without ever knowing anything about avr8-stub.h.

Library is installed via lib_deps git in platformio.ini

2

Does the header file in question have a standard guard? If it does, you can see in your library if it is defined.
#ifndef OTHERHEADER
#define OTHERHEADER
…
#endif
If it used a #pragma once, see if there is a unique define you can use.

4

I can’t imagine how this is supposed to work!

Translation units (.c / .cpp files) are compiled separately. Unless they have a common header file or include the respective header file of the other library, they cannot see each other’s macros.

The only solution I can see would be to define a global macro in platformio.ini (build_flags = -Dsomemacro).

Proof of concept:

Project file structure:

.
├── lib
│   ├── LibA
│   │   ├── LibA.cpp
│   │   └── LibA.h
│   ├── LibB
│   │   ├── LibB.cpp
│   │   └── LibB.h
│   └── README
├── src
│   └── main.cpp
└── platformio.ini

LibA.h

#ifndef _LIB_A_
#define _LIB_A_

const char* functionFromLibA();

#endif

LibA.cpp

#include "LibA.h"

#ifdef _LIB_B_

static const char* message = "LibA: LibB is present";

#else

static const char* message = "LibA: LibB is NOT present";

#endif

const char* functionFromLibA() { return message; }

LibB.h

#ifndef _LIB_B_
#define _LIB_B_

const char* functionFromLibB();

#endif

LibB.cpp

#include "LibB.h"

#ifdef _LIB_A_

static const char* message = "LibB: lib A is present!"

#else

static const char* message = "LibB: lib A is NOT present";

#endif

const char* functionFromLibB() { return message; }

main.cpp

#include <iostream>
#include <LibA.h>
#include <LibB.h>

int main() {
    std::cout << functionFromLibA() << std::endl;
    std::cout << functionFromLibB() << std::endl;
    return 0;
}

platformio.ini

[env:native]
platform = native

Output

LibA: LibB is NOT present
LibB: LibA is NOT present
5

sivar2311 has given an example that demonstrates the shortfall of what I suggested.
But I assure you that a simple scenario like this will work
#include “avr8-stub.h”
#include “myHeaderFile.”
…

File: avr8-stub.h
#ifndef AVR8_STUB_H
#define AVR8_STUB_H
…

File myHeaderFile.h
#if defined(AVR8_STUB_H)
…

If avr8-stub.h uses the #pragma once method this will not work and if you don’t include the header before yours in the same unit, it will not work.
This is the only way I know of to come close to what you want. I’m not aware of any method outside of build configuration files that could do this.