C++: obtaining and printing a function signature

R00ts · 01-02-2008, 03:52 PM

I need to write a wrapper around an API that prints out a message containing the name of the API function invoked, the list of arguments passed, and the return value of the call. I'm wondering if it would be possible to do this a little bit more intelligently than I am right now (I'm currently writing a wrapper function for each API function). Each wrapper function pretty much does the same thing (with a few special case exceptions):

1) Print the name of the API function being called and the values of each argument
2) Call the API function
3) Print the return value of the function
4) If the return value is now what we expected to receive, print an error message

So I can't help but feel there's a better way to do this. Maybe by providing a single generic function for doing the above steps for any API function called. Does anyone have any clever ideas about this? I've been thinking about possible approaches but haven't come up with any good leads. Also I'm trying to avoid unnecessary dependencies in this code (ie, no boost). I'm not sure if there's an answer for this or not, but thanks for any insight you can share with me.

harry edwards · 01-02-2008, 05:58 PM

I believe C++ doesn't cater for what you ask; however, certain compilers supply MACROs which maybe of use. GCC provides three magic variables which hold the name of the current function, as a string. These are:

__func__
__FUNCTION__
__PRETTY_FUNCTION__

others of interest standardized by ANSI C are:

__LINE__
__FILE__
__TIME__
__DATE__

dmail · 01-02-2008, 06:05 PM

If you wrote the API then you could use variables in gcc such as __FUNCTION__ and __PRETTY_FUNCTION__ and on windows the __FUNCTION__ macro. If you did not write the API then I would say you would have to use macros to generate code for you as a proxy function or to generate a template function. The following is untested yet should work, yet it assumes that the parameters and results can be inserted to a stream and they are not member functions.

Code:

#include <iostream>

int test0()
{
 	 std::cout <<"called test0"<<std::endl;
 	 return 0;
}
int test1(int t)
{
 	 std::cout <<"called test1"<<std::endl;
 	 return 1;
}
int test2(int t,int t1)
{
 	 std::cout <<"called test2"<<std::endl;
 	 return 2;
}
int test3(int t,int t1,int t2)
{
 	 std::cout <<"called test3"<<std::endl;
 	 return 3;
}
int test4(int t,int t1,int t2,int t3)
{
 	 std::cout <<"called test4"<<std::endl;
 	 return 4;
}
#define PARAM0()
#define PARAM1(T1 ) T1 p1 
#define PARAM2(T1,T2) PARAM1(T2), T2 p2
#define PARAM3(T1,T2,T3) PARAM2(T1,T2), T3 p3
#define PARAM4(T1,T2,T3,T4) PARAM3(T1,T2,T3), T4 p4


#define PRINT_NAME(Name)std::cout <<#Name <<" "
#define PRINT_AND_RETURN\
		std::cout <<"result: "<<r <<std::endl;\
		if(r != expected)std::cout <<"Error expected " <<expected <<std::endl;\
		return r;
		
#define PRINT_PARAM1(p1_)\
		<<p1_ <<" " 
		
#define PRINT_PARAM2(p1_,p2_)\
		PRINT_PARAM1(p1_) <<p2_ <<" " 
		
#define PRINT_PARAM3(p1_,p2_,p3_)\
		PRINT_PARAM2(p1_,p2_) <<p3_ <<" " 
		
#define PRINT_PARAM4(p1_,p2_,p3_,p4_)\
		PRINT_PARAM3(p1_,p2_,p3_) <<p4_ <<" " 
						
#define PROXY_FUNCTION_0(Return,Name)\
namespace PROXY\
{\
	Return Name(Return expected)\
	{\
		PRINT_NAME(Name)<< std::endl;\
		Return r = ::Name();\
		PRINT_AND_RETURN\
	}\
}
#define PROXY_FUNCTION_1(Return,Name,P1)\
namespace PROXY\
{\
	Return Name( PARAM1(P1),Return expected )\
	{\
		PRINT_NAME(Name)\
		PRINT_PARAM1(p1)<< std::endl;\
		Return r =  ::Name( p1 );\
		PRINT_AND_RETURN\
	}\
}

#define PROXY_FUNCTION_2(Return,Name,P1,P2)\
namespace PROXY\
{\
	Return Name( PARAM2(P1,P2),Return expected )\
	{\
		PRINT_NAME(Name)\
		PRINT_PARAM2(p1,p2)<< std::endl;\
		Return r =  ::Name(p1,p2);\
		PRINT_AND_RETURN\
	}\
}

#define PROXY_FUNCTION_3(Return,Name,P1,P2,P3)\
namespace PROXY\
{\
	Return Name( PARAM3(P1,P2,P3),Return expected )\
	{\
		PRINT_NAME(Name)\
		PRINT_PARAM3(p1,p2,p3)<< std::endl;\
		Return r =  ::Name( p1,p2,p3);\
		PRINT_AND_RETURN\
	}\
}

#define PROXY_FUNCTION_4(Return,Name,P1,P2,P3,P4)\
namespace PROXY\
{\
	Return Name( PARAM4(P1,P2,P3,P4),Return expected )\
	{\
		PRINT_NAME(Name)\
		PRINT_PARAM4(p1,p2,p3,p4)<< std::endl;\
		Return r =  ::Name( p1,p2,p3,p4);\
		PRINT_AND_RETURN\
	}\
}

PROXY_FUNCTION_0(int,test0)
PROXY_FUNCTION_1(int,test1,int)
PROXY_FUNCTION_2(int,test2,int,int)
PROXY_FUNCTION_3(int,test3,int,int,int)
PROXY_FUNCTION_4(int,test4,int,int,int,int)

int main(int argc, char *argv[])
{
 	PROXY::test0(0);
 	PROXY::test1(1,1);
 	PROXY::test2(1,2,2);
 	PROXY::test3(1,2,3,3);
 	PROXY::test4(1,2,3,4,5);// should cause an error
    return 0;
}

dmail · 01-03-2008, 04:02 AM

There are problems with the sample code I posted such as not being able to detect pointers to types instead of types, not using epsilon range checking for floating point types, can not use member functions etc etc these can all be solved but more information would be required such as but not limited to:
How is the api linked?
Is it a c or c++ api?
what types are the parameters?
Do you have a functor library, if not could you not use loki's(headers only)?
Because I am nosey

which API is it?

R00ts · 01-07-2008, 11:54 AM

Sorry I've been busy the past few days and haven't gotten around to reading this thread. Thanks for the responses.

Quote:

Originally Posted by dmail

How is the api linked?
Is it a c or c++ api?
what types are the parameters?
Do you have a functor library, if not could you not use loki's(headers only)?
Because I am nosey

which API is it?

- dynamically linked I believe
- C
- mostly integer types and pointers. No floating point
- I can't add any library dependencies

The API is device driver software for VXI controllers. The code I'm writing has to work for Windows, Linux, OS X, Solaris, VxWorks, Pharlap, and possibly other OSes. Of course, this means it also needs to work with various compilers. I've decided to go ahead and just do it the tedious manual way, as there are some specific scenarios where I want the wrapper function to do something atypical. Thanks for the help though