C++ error: ‘char8_t’ was not declared in this scope

The error 'char8_t' was not declared in this scope occurs in C++ when the program attempts to use the char8_t type without the necessary C++20 standard enabled or in an older compiler that does not support C++20. The char8_t type was introduced in C++20 as a distinct type for UTF-8 character literals and strings, and using it without proper configuration leads to this error.

This tutorial explains why this error occurs, how to resolve it, and provides examples with solutions.

Why This Error Occurs

The following are some of the reasons why this error can occur.

  1. The char8_t type is introduced in the C++20 standard. If your compiler is not set to use C++20, the char8_t type will not be recognized.
  2. Using an older compiler that does not support the C++20 standard can also cause this error.
  3. In some cases, even with a modern compiler, the char8_t type might be disabled if the standard version is not explicitly specified.

How to Resolve the Error

The following are the possible solutions to resolve this error.

  1. Ensure that you are using a compiler that supports C++20. Popular compilers like GCC (>=9.1), Clang (>=10), and MSVC (>=2019) support C++20.
  2. Explicitly enable the C++20 standard in your compiler settings or during compilation: For GCC or Clang, use the -std=c++20 flag: g++ -std=c++20 -o program program.cpp
  3. Check your build system or IDE configuration and set the language standard to C++20.
  4. Update your compiler to the latest version if it does not support C++20.

Examples

Example 1: Program Using char8_t Without Proper Configuration

This program demonstrates the use of char8_t without enabling C++20.

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#include <iostream>
using namespace std;

int main() {
    char8_t ch = u8'A'; // UTF-8 character
    cout << ch << endl;
    return 0;
}

Error Output:

error: 'char8_t' was not declared in this scope

Solution:

  1. Enable C++20 by compiling the program with the -std=c++20 flag:
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g++ -std=c++20 -o program program.cpp

Example 2: Correctly Configured Program

This program demonstrates the proper use of char8_t with the correct C++20 standard enabled.

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#include <iostream>
using namespace std;

int main() {
    char8_t ch = u8'A'; // UTF-8 character
    cout << (char)ch << endl; // Cast to char for output
    return 0;
}

Output:

A

Explanation:

  1. The char8_t type is correctly recognized because C++20 is enabled.
  2. The variable ch is assigned a UTF-8 character, and the cast to char ensures compatibility with std::cout.

Key Points to Remember about char8_t data type

  1. char8_t is a data type introduced in C++20 for handling UTF-8 encoded characters.
  2. Using char8_t requires enabling the C++20 standard in your compiler.
  3. Ensure your compiler supports C++20, and use the appropriate flag (-std=c++20) during compilation.
  4. Update to the latest version of your compiler if it does not support C++20 features.