How can I call function with current function name in C, C++?

Question

before start, sorry for my poor English. Environment: c, c++, VS2019, after C99

Problem: I have to call functions which have named with prefix with callee name. I have many callee and variable prefix, so I want to handle it macro in preprocess-time for convenience with coding.

I tried:

`void prefix_function_name();
 void function_name(){
     (prefix_##__func__)();
 }
`

I know it can't be possible, cause func is const char[].

So I need to : get function name with a token not a string. or : turn a string into a token. ex)

void foo(); const char[] a = "foo"; 
a();

Is anyone have solution?

Here's my actual problem.

I have many functions with C code. And I'm going to make test code with gtest(C++). And I need to use mock(or stub. anyway) for functions. But, there is no way to call mock function instead of original function. So I need to make hook like this

`extern "C" void mock_foo();
 void foo(){
     return mock_foo(); // hook
     ... // actual code
 }
`

To avoid miss typing and human error, I wanted to make macro that makes hook for functions. Now I'm using macro like this. (Not in detail)

`#define MACRO(func_name) return mock_##func_name();
 void foo(){
     MACRO(foo) // hook
     ... // actual code
 }
`

And I wanted to get rid of typing function name.

Here's my actual problem. Is there any way?

what langauge is this? Please pick one. And this looks like a xy problem. Why do you need this? How is (prefix_##__func__)(); (assuming it would work) any better than prefix_function_name() ? — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Jul 9, 2021 at 8:30
i mean inside function_name the name of the current function is always function_name no macros or runtime effects can change that — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Jul 9, 2021 at 8:31
i guess its one of the lessons one has to learn the hard way: Macros are not convenient for coding, rather the opposite. It took me a while to get convinced, because at first they look pretty cool — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Jul 9, 2021 at 8:42
I second the above comments: you probably try to solve your problem a wrong way. Please describe the actual problem, only then an appropriate way to solve it can be chosen. — CiaPan
– CiaPan, Commented Jul 9, 2021 at 8:48

Peter · Accepted Answer · 2021-07-09 08:52:16Z

3

You can't do it the way you describe, since there is no way to turn a string (variable or literal) into a token. You might try a macro that defines your calling function, such as

#define DEFINE_FUNCTION(prefix, name)  void name () { prefix ##_ ##name ();}

and use it

void foo_func() {std::cout << "foo_func()\n";}     // assume <iostream> has been included

DEFINE_FUNCTION(foo, func)           // note no ; here

int main()
{
     func();       
}

This will work since DEFINE_FUNCTION(foo, func) has defined func() so it calls foo_func().

Generally I would strongly advise against doing the above. It may seem convenient to you now to use a macro, rather than defining your functions by hand. It will not seem so convenient in future when you, or someone else, is maintaining/extending the code - particularly if some of the functions needs to do things slightly differently than the macro sets up. Your code will quickly become a mess in that case.

answered Jul 9, 2021 at 8:52

Peter

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1 Comment

jinwook Over a year ago

Yes. Maybe I should use more manpower. I can use #define MACRO(prefix, funcname) instead of #define MACRO(prefix). I just wanted to use "__func__" instead of manpower.

ZacharyLiu · Accepted Answer · 2021-07-09 08:43:55Z

0

maybe you want this:

void prefix_function_name();
#define INVOKER_FUNCTION(name) \
void name () {\
   prefix_##name();\
}

INVOKER_FUNCTION(function_name);

answered Jul 9, 2021 at 8:43

ZacharyLiu

419 bronze badges

3 Comments

M. Zhang Over a year ago

The OP wants to use a C-string as the function name, so this answer is probably not the case.

Peter Over a year ago

@M.Zhang - That's not what the OP asked for. The question is about how to get func() to call prefix_func(). The description in terms of a string literal is because the OP's first thought was to use the __func__ predefined macro (which gives a nul terminated string) to recover the name of the function as a token - and even the OP admits that is not possible.

jinwook Over a year ago

Peter is right. I already have function and want to call other function in the function with the function name.

Evgeny · Accepted Answer · 2021-07-09 08:39:50Z

-1

I'm afraid, you have selected slightly-not-suitable language (i mean C++). But, You can do this (in C++) by using dll-s:

pack your functions into external library (.dll, .so).
then you can load library and export function by name and call it. See boost::dll:import_alias (for crossplatform code), LoadLibrary and GetProcAddress (for Windows).

answered Jul 9, 2021 at 8:39

Evgeny

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1 Comment

jinwook Over a year ago

Thanks for answering, but it would be too load. I just wanted to make macro for convenience. Repeatedly, thanks for answering. I would find this later.

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