Is it possible to write a varargs function that sends it argument list to another varargs function?

c++ variadic-functions
gct picture gct · Jan 13, 2010 · Viewed 19.3k times · Source

Possible Duplicate:
C Programming: Forward variable argument list.

What I'd like to do is send data to a logging library (that I can't modfify) in a printf kind of way.

So I'd like a function something like this:

void log_DEBUG(const char* fmt, ...) {
   char buff[SOME_PROPER_LENGTH];
   sprintf(buff, fmt, <varargs>);
   log(DEBUG, buff);
}

Can I pass varargs to another vararg function in some manner?

Answer

John Dibling picture John Dibling · Jan 13, 2010

You can't forward the variable argument list, since there's no way to express what's underneath the ... as a parameter(s) to another function.

However you can build a va_list from the ... parameters and send that to a function which will format it up properly. This is what vsprintf is for. Example:

void log_DEBUG(const char* fmt, ...) {
   char buff[SOME_PROPER_LENGTH];
   va_list args;
   va_start(args, fmt);
   vsprintf(buff, fmt, args);
   va_end(args);
   log(DEBUG, buff);
}

Related questions

Variable number of arguments in C++?

How can I write a function that accepts a variable number of arguments? Is this possible, how?

Read More
How to pass variable number of arguments to printf/sprintf

I have a class that holds an "error" function that will format some text. I want to accept a variable number of arguments and then format them using printf. Example: class MyClass { public: void Error(const char* format, ...); }; The Error …

Read More
Passing variable arguments to another function that accepts a variable argument list

So I have 2 functions that both have similar arguments void example(int a, int b, ...); void exampleB(int b, ...); Now example calls exampleB, but how can I pass along the variables in the variable argument list without modifying exampleB (as …

Read More