c pass newly created vector as parameter-CodePudding

If I have a function that expects a std::pair or std::array for example, I can do the following:

#include <array>
#include <string>

void foo(std::array<int,5>){}
void bar(std::pair<int,std::string>){}

int main(){

foo({1,2,3,4,5});
bar(std::make_pair(1, "test"));

}

What would be a similiar way of passing a std::vector as a parameter? Is there a way to pass a std::vector that is beeing created in the same line as the call to a function that expects it as a parameter?

How to achieve the requested with the following:

#include <vector>
#include <string>

void testVector(std::vector<std::string> &t){}

int main(){

std::vector<std::string> boring; // I dont want to create a vector like this
testVector(boring); // this works obviously

testVector({"hello"}); //this does not work
testVector(std::vector<std::string>(){"test"}); // does not work aswell 

}

I just edited the question because I wanted to pass a reference. But I think there is no way of passing a reference to a vector that was instantiated that way right?

CodePudding user response：

using

void baz(std::vector<int> vec) { … }

works:

…
baz({1,2,3});
…

But: using a plain vector as signature will lead to every function call making a copy of the vector. You very rarely actually want that, unless your method actually needs a copy for some reason.

The usual way is to use a reference:

void baz_ref(std::vector<int>& vec) { … }

which means that now, the function doesn't get a copy, but works on the original vector – but that means your function might have side effects that the calling function doesn't expect!

Also, you can't call baz_ref({1, 2, 3});, because that would pass a reference to a temporary object.

In cases where your function doesn't need to modify the vector:

void baz_constref(const std::vector<int>& vec) { … }

is the way to go – no copy, trying to modify vec won't work. The compiler can beautifully optimize this, and you can also call baz_constref({1, 2, 3});.

There's another option: Move semantics, and it might be the right thing if your function actually modifies the vector – should that function be the new "owner"? Then, you should move that vector into the function, but the calling function then loses the ability to use it.

CodePudding user response：

Firstly your entry point is wrong, it should be int main and not void main. And the following code works

#include <vector>
#include <string>

void testVector(std::vector<std::string>){}

int main()
{

    std::vector<std::string> boring;
    testVector(boring);

    testVector({"hello"}); // This works
    testVector(std::vector<std::string>{"test"}); // This works too :)
}

Here is the test of the above code