C uniform declaration is not working in class-CodePudding

I am trying to have a member array in a class with its length specified by the const static int variable for future needs.

My compiler throws an error with it, and I am not sure this is an error about a uniform initialization or array initialization, or both.

Here is the header file:

#ifndef SOUECE_H
#define SOURCE_H

class Test
{
public:
    Test();
    static const int array_length{2};
    double array[array_length];
};

#endif

This is the source file.

#include "source.h"

Test::Test()
    :array_length{0} //Typo of array{0}
{
}

These are the problem messages.
[enter image description here][1] [1]: https://i.stack.imgur.com/IQ2Mk.png

This is the CMake file.

cmake_minimum_required(VERSION 3.0.0)
project(temp VERSION 0.1.0)

include(CTest)
enable_testing()

add_executable(temp main.cpp)

set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)

Finally, these are what the compiler is complaining about when I try to build the project.

[main] Building folder: temp 
[build] Starting build
[proc] Executing command: /usr/local/bin/cmake --build /Users/USERNAME/Desktop/temp/build --config Debug --target all -j 14 --
[build] [1/2  50% :: 0.066] Building CXX object CMakeFiles/temp.dir/main.cpp.o
[build] FAILED: CMakeFiles/temp.dir/main.cpp.o 
[build] /usr/bin/clang     -g -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk -MD -MT CMakeFiles/temp.dir/main.cpp.o -MF CMakeFiles/temp.dir/main.cpp.o.d -o CMakeFiles/temp.dir/main.cpp.o -c ../main.cpp
[build] In file included from ../main.cpp:1:
[build] ../source.h:8:22: error: function definition does not declare parameters
[build]     static const int array_length{2};
[build]                      ^
[build] ../source.h:9:18: error: use of undeclared identifier 'array_length'
[build]     double array[array_length];
[build]                  ^
[build] 2 errors generated.
[build] ninja: build stopped: subcommand failed.
[build] Build finished with exit code 1

I am using macOS 12.0 beta, with VS Code 1.60.2, clang 13.0.0, CMake 3.20.2.

Please let me know if you see any wrong or have any suggestions.

CodePudding user response：

This cannot work:

Test::Test()
    :array_length{0}

You cannot set a const static data member in your constructor. A static value has the same value accross all object instances. But as it is also const no instance is allowed to change the value.

CodePudding user response：

Since array_length is static const you have to initialize it like this:

source.h

#ifndef SOUECE_H
#define SOURCE_H

class Test
{
public:
    Test();
    static const int array_length = 2;
    //static const int array_length{2}; this will also work just note that we cannot use constructor initializer list to initialize static data members
    double array[array_length];
};

#endif

source.cpp

#include "source.h"

Test::Test()//we cannot use constructor initializer list to initialize array_length
    
{
}

Note that static const int array_length{2}; will also work but the thing is that in the constructor we cannot use constructor initializer list to initialize static data member.

EDIT: If you decide to use static const int array_length{2}; then make sure that you have C 11(or later) enabled in your CMakeLists.txt. For this you can add

set (CMAKE_CXX_STANDARD 11)

to your CMakeLists.txt.

Alternatively, you could instead add

target_compile_features(targetname PUBLIC cxx_std_11)

in your CMakeLists.txt. In your case replace targetname with temp since that is the targetname that you have.