I just got some C code that uses extern "C" to declare external functions like this:
extern "C" void func(); Is this valid C? I'm getting an error at this line, but I'm not sure if it's because of this or something else.
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3 Answers
No, it's not valid C. It should only be used in C++ code to refer to functions defined in C code. The extern "C" should be surrounded in a ifdef __cplusplus/#endif block:
// For one function #ifdef __cplusplus extern "C" #endif void func(); // For more than one function #ifdef __cplusplus extern "C" { #endif void func1(); void func2(); #ifdef __cplusplus } #endif 
Comments
this is a C++ notation to tell the compiler/linker to use C calling standards.
Usually that line is wrapped in an pre-processor statement.
#ifdef __cplusplus extern "C" { #endif // stuff #ifdef __cplusplus } #endif 
Comments
Not valid in C. If present after preprocessing this will result in a diagnostic as per the standard.
For C++, this turns of name-mangling. See this for more details as to why it may be required. Can you post some more details?
