How to wrap a function with variable length arguments?

Question

I am looking to do this in C/C++.

I came across Variable Length Arguments but this suggests a solution with Python & C using libffi.

Now, if I want to wrap printf function with myprintf

What I do is like below:

void myprintf(char* fmt, ...) {     va_list args;     va_start(args,fmt);     printf(fmt,args);     va_end(args); }  int _tmain(int argc, _TCHAR* argv[]) {     int a = 9;     int b = 10;     char v = 'C';     myprintf("This is a number: %d and \nthis is a character: %c and \n another number: %d\n",a, v, b);     return 0; } 

But the results are not as expected!

This is a number: 1244780 and this is a character: h and another number: 29953463 

Any point where did I miss??

Answer 1

the problem is that you cannot use 'printf' with va_args. You must use vprintf if you are using variable argument lists. vprint, vsprintf, vfprintf, etc. (there are also 'safe' versions in Microsoft's C runtime that will prevent buffer overruns, etc.)

You sample works as follows:

void myprintf(char* fmt, ...) {     va_list args;     va_start(args,fmt);     vprintf(fmt,args);     va_end(args); }  int _tmain(int argc, _TCHAR* argv[]) {     int a = 9;     int b = 10;     char v = 'C';      myprintf("This is a number: %d and \nthis is a character: %c and \n another number: %d\n",a, v, b);     return 0; } 

Answer 2

In C++11 this is one possible solution using Variadic templates:

template<typename... Args> void myprintf(const char* fmt, Args... args ) {     std::printf( fmt, args... ) ; } 

EDIT

As @rubenvb points out there are trade-offs to consider, for example you will be generating code for each instance which will lead to code bloat.