How Are The __cplusplus Directive Defined In Various Compilers?

Apr 26, 2025 by ADMIN 64 views

How are the __cplusplus Directive Defined in Various Compilers?

Introduction

The __cplusplus directive is a preprocessor macro in C++ that provides information about the version of the C++ compiler being used. This macro is defined by the compiler and can be used by developers to write code that is compatible with different versions of the C++ standard. In this article, we will explore how the __cplusplus directive is defined in various compilers and what it signifies.

What is the __cplusplus Directive?

The __cplusplus directive is a preprocessor macro that is defined by the compiler. It is used to provide information about the version of the C++ compiler being used. The value of this macro is typically a numeric value that represents the version of the C++ standard being used.

How is the __cplusplus Directive Defined in Various Compilers?

The __cplusplus directive is defined differently in various compilers. Here are some examples:

GCC Compiler

In the GCC compiler, the __cplusplus directive is defined as follows:

For C++98: __cplusplus = 199711L
For C++11: __cplusplus = 201103L
For C++14: __cplusplus = 201402L
For C++17: __cplusplus = 201703L
For C++20: __cplusplus = 202002L

Clang Compiler

In the Clang compiler, the __cplusplus directive is defined as follows:

For C++98: __cplusplus = 199711L
For C++11: __cplusplus = 201103L
For C++14: __cplusplus = 201402L
For C++17: __cplusplus = 201703L
For C++20: __cplusplus = 202002L

Microsoft Visual C++ Compiler

In the Microsoft Visual C++ compiler, the __cplusplus directive is defined as follows:

For C++98: __cplusplus = 199711L
For C++11: __cplusplus = 201103L
For C++14: __cplusplus = 201402L
For C++17: __cplusplus = 201703L
For C++20: __cplusplus = 202002L

What Does the Expansion of __cplusplus Signify?

The expansion of the __cplusplus directive signifies the version of the C++ standard being used. Here are some examples:

__cplusplus = 199711L: This signifies that the code is being compiled with the C++98 standard.
__cplusplus = 201103L: This signifies that the code is being compiled with the C++11 standard.
__cplusplus = 201402L: This signifies that the code is being compiled with the C++14 standard.
__cplusplus = 201703L: This signifies that the code is being compiled with the C++17 standard.
__cplusplus = 202002L: This signifies that the code is being compiled with the C++20 standard.

What are the Possible Expansions of this Macro?

The possible expansions of the __cplusplus macro are as follows:

199711L: This signifies the C++98 standard.
201103L: signifies the C++11 standard.
201402L: This signifies the C++14 standard.
201703L: This signifies the C++17 standard.
202002L: This signifies the C++20 standard.

Conclusion

In conclusion, the __cplusplus directive is a preprocessor macro that provides information about the version of the C++ compiler being used. The value of this macro is typically a numeric value that represents the version of the C++ standard being used. The expansion of this macro signifies the version of the C++ standard being used, and it can be used by developers to write code that is compatible with different versions of the C++ standard.

Example Use Case

Here is an example use case of the __cplusplus directive:

#include <iostream>
int main() 
#ifdef __cplusplus
if (__cplusplus >= 201103L) {
std:cout << "This code is being compiled with C++11 or later." << std::endl;
 else 
std:cout << "This code is being compiled with C++98 or earlier." << std::endl;

#endif
return 0;
}

In this example, the __cplusplus directive is used to check if the code is being compiled with C++11 or later. If it is, then a message is printed to the console indicating that the code is being compiled with C++11 or later. Otherwise, a message is printed indicating that the code is being compiled with C++98 or earlier.

References

Introduction

The __cplusplus directive is a preprocessor macro in C++ that provides information about the version of the C++ compiler being used. In our previous article, we explored how the __cplusplus directive is defined in various compilers and what it signifies. In this article, we will answer some frequently asked questions about the __cplusplus directive.

Q: What is the purpose of the __cplusplus directive?

A: The purpose of the __cplusplus directive is to provide information about the version of the C++ compiler being used. This information can be used by developers to write code that is compatible with different versions of the C++ standard.

Q: How is the __cplusplus directive defined in different compilers?

A: The __cplusplus directive is defined differently in different compilers. For example, in the GCC compiler, the __cplusplus directive is defined as follows:

For C++98: __cplusplus = 199711L
For C++11: __cplusplus = 201103L
For C++14: __cplusplus = 201402L
For C++17: __cplusplus = 201703L
For C++20: __cplusplus = 202002L

Q: What does the expansion of __cplusplus signify?

A: The expansion of the __cplusplus directive signifies the version of the C++ standard being used. For example:

__cplusplus = 199711L: This signifies that the code is being compiled with the C++98 standard.
__cplusplus = 201103L: This signifies that the code is being compiled with the C++11 standard.
__cplusplus = 201402L: This signifies that the code is being compiled with the C++14 standard.
__cplusplus = 201703L: This signifies that the code is being compiled with the C++17 standard.
__cplusplus = 202002L: This signifies that the code is being compiled with the C++20 standard.

Q: Can I use the __cplusplus directive to check if my code is being compiled with a specific version of the C++ standard?

A: Yes, you can use the __cplusplus directive to check if your code is being compiled with a specific version of the C++ standard. For example:

#include <iostream>
int main() 
#ifdef __cplusplus
if (__cplusplus >= 201103L) {
std:cout << "This code is being compiled with C++11 or later." << std::endl;
 else 
std:cout << "This code is being compiled with C++98 or earlier." << std::endl;

#endif
return 0;
}

Q: Are there any limitations to using the __cplusplus directive?

A: Yes, there are some limitations to using the __cplusplus directive. For example:

The__cplusplus` directive is only defined in the preprocessor, so you cannot use it in the compiler itself.
The __cplusplus directive is only defined for C++ compilers, so you cannot use it with other languages.
The __cplusplus directive is only defined for compilers that support the C++ standard, so you cannot use it with compilers that do not support the C++ standard.

Q: Can I use the __cplusplus directive in a header file?

A: Yes, you can use the __cplusplus directive in a header file. However, you should be careful when using the __cplusplus directive in a header file, as it can cause problems if the header file is included in multiple translation units.

Q: Can I use the __cplusplus directive to check if my code is being compiled with a specific compiler?

A: No, you cannot use the __cplusplus directive to check if your code is being compiled with a specific compiler. The __cplusplus directive only provides information about the version of the C++ standard being used, not the compiler being used.

Q: Can I use the __cplusplus directive to check if my code is being compiled with a specific platform?

A: No, you cannot use the __cplusplus directive to check if your code is being compiled with a specific platform. The __cplusplus directive only provides information about the version of the C++ standard being used, not the platform being used.

Conclusion

In conclusion, the __cplusplus directive is a preprocessor macro in C++ that provides information about the version of the C++ compiler being used. It can be used to write code that is compatible with different versions of the C++ standard. However, there are some limitations to using the __cplusplus directive, and you should be careful when using it in a header file.