I have a function:
vector<int> prime(int num, ...) {
vector<int> mas;
va_list args;
va_start(args, num);
for (int i = 0; i < num; i++) {
int v = va_arg(args,int);
if (isPrime(v)){
mas.push_back(v);
}
}
cout << endl;
va_end(args);
return mas;}
It should detected prime numbers. But when i call it, part of my numbers, don`t get over.
It looks something like this
Input: 5, 7, 10, 15, 20,12, 13,16,19
Numbers what cout returns in the loop: 7,7
Help pls!
First of all Variadic arguments from C are considered a bad practice in C++ and should be avoided.
There are plenty of better C++ solutions which are able to replace this C feature.
Old fashioned std::vector:
std::vector<int> filterPrimes(std::vector<int> a) {
auto end = std::remove_if(a.begin(), a.end(), [](auto x) {
return !isPrime(x)
};
a.remove(end, a.end());
return a;
}
Or std::initializer_list
std::vector<int> filterPrimes(std::initializer_list<int> l) {
std::vector<int> r;
std::copy_if(l.begin(), l.end(), std::back_inserter(r), isPrime);
return r;
}
Or Variadic templates, or template with iterator ranges, or ... .
If the arguments are all of the same type, then just pass them in as, say, a vector.
#include <vector>
#include <iostream>
using namespace std;
void func(const vector<int>& args)
{
for (size_t i = 0; i < args.size(); i++)
cout << args[i] << endl;
}
int main(void)
{
vector<int> v = { 5, 7, 10, 15, 20, 12, 13, 16, 19 };
func(v);
return 0;
}
std::initializer_list. I also believe that va_arg is the only reasonable way to do this at runtime if the types differ.
va_arg(args, int)3*n times. How is it supposed to know that the first three calls should return the first argument, the second three should return the second argument, and so on? It burns through all arguments in n/3 iterations, and then UB happens. You need to call it one per iteration, and save the result to a variable.const std::vector<int> &as a parameter (or, in C++20,std::span<const int>), or, if you absolutely want the same call syntax you have now, use variadic templates.