52391

Using a function with variable argument strings

I was playing around a bit with functions with variable arguments, and decided to make a function to create vectors with the arguments. My function for creating an int vector worked...

vector<int> makeIntVector(int numArgs, ...) { va_list listPointer; va_start(listPointer, numArgs); vector<int> made; for(int a = 0; a < numArgs; a++) made.push_back(va_arg(listPointer, int)); va_end(listPointer); return made; }

but not my function for creating a string vector:

vector<string> makeStringVector(int numArgs, string something, ...) { va_list listPointer; va_start(listPointer, something); vector<string> made; for(int a = 0; a < numArgs; a++) made.push_back(va_arg(listPointer, string)); va_end(listPointer); return made; }

which crashes the program. What am I doing wrong?

Answer1:

Attempting to pass a string as a varaidic parameter gives undefined behavior: "If the argument has a non-POD class type (clause 9), the behavior is undefined." (§5.2.2/7 of the standard).

Answer2:

Variable arguments functions should not be used in C++.

The first argument is that they are only safe for PODs like int or char*, passing a non-POD C++ type has undefined behaviour.

Instead of creating a function with a long list of arguments, why don't you just create a vector and push back your strings into it?

Answer3:

I am not sure but I would investigate the fact that va_* are macros, int a "primitive" type while string is not. Maybe this causes the problem somewhere.

EDIT: g++ gives an important warning: cannot receive objects of non-POD type ‘struct std::string’ through ‘...’; call will abort at runtime

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