unresolved external symbol, c (not c++)

Question

hi, I am trying to convert some code from c++ to pure c, or at least most of it

When I had things in c++ I could make a .h file, then a .cpp file and simply type the implementation of functions declared in the .h in the .cpp; I did not have to edit linker files or anything like that, and the ide would keep track of it all, and I had no linker problems even if a function was not a member of a class

Now I have a .h, but when I try to use a function defined in the .c, which is declared in the .h, I get a LNK2019 unresolved external symbol "void __cdecl LC_iniciar_trace(char const *)" (?LC_iniciar_trace@@YAXPBD@Z) referenced in function _wWinMain@16 LC 1 C:\Users\xxxxx\Documents\Proyectos\plataforma multimedia c puro v1\Visual Studio\LC 1\LC 1.obj

Why is in not able to see the function implemented in a .c file in the same project? If I make a syntax error in the function the compiler would give an error, so is not as if the compiler does not see the .c file or anything like that

tnx

Answer 1

Maybe the name of the function in .c file is different.

Or, if you are trying to use the function in .cpp files, then try this form of #include (in .cpp files only):

extern "C"
{
   #include "MyHeaderFile.h"
}

Answer 2

Hi, thank you both. By just changing the extension from .c to .cpp the errors stopped, but I willl use the extern c suggestion, thanks

Answer 3

In case you haven't discovered why you needed the changes to eliminate the link error(s), the following references should help clarify the issue.

Name Decoration

https://learn.microsoft.com/en-us/cpp/error-messages/tool-errors/name-decoration?view=msvc-170

"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 linker names you don't expect."

Decorated names

https://learn.microsoft.com/en-us/cpp/build/reference/decorated-names?view=msvc-170

"Functions, data, and objects in C and C++ programs are represented

internally by their decorated names. A decorated name is an encoded

string created by the compiler during compilation of an object, data,

or function definition. It records calling conventions, types, function

parameters and other information together with the name. This name

decoration, also known as name mangling, helps the linker find the

correct functions and objects when linking an executable."

extern (C++)

https://learn.microsoft.com/en-us/cpp/cpp/extern-cpp?view=msvc-170

"extern "C" specifies that the function is defined elsewhere and uses

the C-language calling convention. The extern "C" modifier may also

be applied to multiple function declarations in a block."

Advanced detailed explanation:

Visual C++ name mangling

https://en.wikiversity.org/wiki/Visual_C%2B%2B_name_mangling

• Wayne