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Name decoration usually refers to C++ naming conventions, but can apply to a number of C cases as well. By default, C++ uses the function name, parameters, and return type to create a linker name for the function. Consider the following function:
void CALLTYPE test(void)
The following table shows the linker name for various calling conventions.
Calling convention |
extern "C" or .c file |
.cpp, .cxx or /TP |
|---|---|---|
C naming convention (__cdecl) |
_test |
?test@@ZAXXZ |
Fastcall naming convention (__fastcall) |
@test@0 |
?test@@YIXXZ |
Standard Call naming convention (__stdcall) |
_test@0 |
?test@@YGXXZ |
Vectorcall naming convention (__vectorcall) |
test@@0 |
?test@@YQXXZ |
Use extern "C" to call a C function from C++. Extern "C" forces use of the C naming convention for non-class C++ functions. Be aware of compiler switches /Tc or /TP, which tell the compiler to ignore the filename extension and compile the file as C or C++, respectively. These options may cause names you do not expect.
Having function prototypes that have mismatched parameters can also cause this error. Name decoration incorporates the parameters of a function into the final decorated function name. Calling a function with the parameter types that do not match those in the function declaration may also cause LNK2001.
There is currently no standard for C++ naming between compiler vendors or even between different versions of a compiler. Therefore linking object files compiled with other compilers may not produce the same naming scheme and thus causes unresolved externals.