When Should I Use `extern 'C'` in C ?

Understanding the Need for extern "C" in C

C and C share similarities in syntax, but their compilation processes diverge significantly. Compiling a header file with a C compiler expects C code. However, when including a header that adheres to C standards, it becomes necessary to explicitly define it using the "extern "C"" directive.

This directive instructs the compiler to assume that the header follows the C Application Binary Interface (ABI). Without it, the linker may encounter incompatibilities, as C 's ABI typically modifies function names with name mangling.

To resolve these issues, follow these steps:

1. When to Use extern "C": Utilize "extern "C"" when including any C header file in a C program.
2. Compiler/Linker Behavior: Using "extern "C"" signals to the compiler that the included header follows C's ABI. This prevents name mangling and ensures compatibility with functions that expect C data structures.
3. Compilation/Linking Solution: By specifying "extern "C"", the compiler processes the header as C code, eliminating the mismatch between the expected C ABI and the modified C ABI. This enables seamless linking of C functions within a C program.

Remember, for most system headers, the "extern "C"" directive is already present, as they are designed to support inclusion in both C and C code. Therefore, it's crucial to use this directive when manually including C headers to avoid potential linker errors.

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