2 replies to this topic

[csepraveenkumar]

When we use va_list in function in c to make it accept a variable number of arguments , the first argument that we give which starts the list of arguments invariable in one form or another specifies the number or the type or both things about the arguments that are going to follow. Isn't there any way in which we don't have to specify this information before hand?

[kernelcoder]

No -- there is no way. We have to have at-least one argument (but can be more than one) before the 3 dots. The second argument to va_start macro must be the argument before the variable arguments. Again, the arguments before the 3 dots can be of any type. There is not relation between the types of variable number of arguments and the immediate before argument to the variable arguments. The macro uses that argument just to determine where to start from for the variable number of arguments.

[rocketboy9000]

For any given call of the variable argument function, it must find out somehow how many arguments it has been given. If your arguments are going to mark the end, rather than the beginning of the list, try this:

#define foo(...) foo_internal(0,__VA_ARGS__);
foo_internal(int dummy,...);

Be very careful.