How to deal with multiple types on var_arg in c++? [closed]

C-style variadic arguments don't carry any type information with them. Your function has to know what args are there before trying to read them. For instance, printf uses the format string to determine what types of arguments are present. You could do something similar, i.e.

long test_long(std::string_view types, ...)
{
    va_list args;
    va_start(args, types);
    for (char c : types) {
        if (c == 'l') {
            long l = va_arg(args, long);
            // do something with l
        } else if (c == 's') {
            const char* s = va_arg(args, const char*);
            // do something with s
        } else {
            // unknown type
            return 0;
        }
    }
    return 1;
}

int main()
{
    test_long("llsl", 0, 1, "yes", 3);
}

Demo

This is fairly brittle though, and you have to explicitly handle every possible type.

A more C++-style approach would be to use a variadic template instead of C-style va_args. For instance:

template <typename... Args>
long test_long(Args... args)
{
    bool results[] = { test_bool(args)... };
    // do something with the results
    return 1;
}

int main()
{
    test_long(0, 1, "yes", 3);
}

Demo

This may be a bit more complex simply due to C++ templates being complex, but its far more type safe than the C-style approach since the type of arguments isn't lost.

In embedded context this may have the downside of increasing code size though, since each different set of parameter types results in a separate function being instantiated from the template.