CODEWITHSUNDEEP
c++gcccmakec++17
Anubis
Anubis

Reputation: 7435

[[maybe_unused]] attribute not working

I am trying to ignore the unused parameter warning using the new c++17 attribute [[maybe_unused]], as below.

int main([[maybe_unused]] int argc, char** argv)
{
    //...
}

But I still get warning: unused parameter ‘argc’ [-Wunused-parameter] with the following additional warning.

warning: ‘maybe_unused’ attribute directive ignored [-Wattributes]

I'm using g++ (GCC) 7.2.0 with cmake-3.11.3. My compiler flags are as follows.

-std=c++17 -Wall -pedantic -Wextra -Weffc++

I remember using this attribute successfully before, but I have no idea why this is not working now. Could someone show what I am doing wrong here?

Upvotes: 10

Views: 5129

Answers (2)

serkan
serkan

Reputation: 131

I tried the code but did not receive any warnings.

  • main.cpp
#include <iostream>

int main([[maybe_unused]] int argc, [[maybe_unused]]char** argv)
{
    return 0;
}
  • CMakeLists.txt
cmake_minimum_required(VERSION 3.1)
project(example)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic -Weffc++)
endif()

add_executable(${PROJECT_NAME} main.cpp)
  • Build
cmake -B build
cd build
make

Note: You can also solve the problem by using (void) as a second method

g++ --version
g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0

cmake --version
cmake version 3.22.1

Upvotes: 0

Andrey Starodubtsev
Andrey Starodubtsev

Reputation: 5292

You can suppress warning about unused variable this way:

int main(int /* argc */, char** argv)
{
    //...
}

or using following trick:

int main(int argc, char** argv)
{
    (void)argc;

    //...
}

In this case this code will work for earlier versions of C++ standard and even for pure C.

Upvotes: 0

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