How to properly handle if a function exits without encoutering a return

Question

I have a function that search a vector and returns the item if it is found. But I want to know that best software appraoch to handle if it is not found.

I have created a function and could return -1 or something but that wouldn't match the return type.

koalaGraph::PVertex Koala::lookUpVertexbyName(const std::string&vertexName, const std::vector<koalaGraph::PVertex>& koalaVertices) {

    for (size_t i = 0; i < koalaVertices.size(); i++) {

        if(koalaVertices[i]->info.name == vertexName) 
            return koalaVertices[i];
    }
}

If a situation is encountered where the item being searched for is not in the vector then program will exit.

Answer 1

You can use std::optional

#include <optional>
std::optional<koalaGraph::PVertex> 
Koala::lookUpVertexbyName(const std::string&vertexName, 
                          const std::vector<koalaGraph::PVertex>& koalaVertices) {

    for (size_t i = 0; i < koalaVertices.size(); i++) {

        if(koalaVertices[i]->info.name == vertexName) 
            return koalaVertices[i];
    }
    return {};
}

int main()
{
    Koala k;
    //...
    auto maybeVertex = k.lookUpVertexByName("foo",vertices);
    if(maybeVertex)
        koalaGraph::PVertex&& vertex = *maybeVertex;
    //alternatively
    if(maybeVertex.has_value())
        //found
}

Answer 2

You could use a for-loop and return a iterator.

std::vector<koalaGraph::PVertex>::const_iterator
Koala::lookUpVertexbyName(
        const std::string&vertexName, 
        const std::vector<koalaGraph::PVertex>& koalaVertices) 
{
    for(auto iter = koalaVertices.begin(); iter != koalaVertices.end(); ++iter) {
        if(koalaVertices[i]->info.name == vertexName) {
            return iter;
        }
    }
    return koalaVertices.end();
}

Further you check if you got end back. end indicates if the value was found or not.

auto iter = <fucntioncall> // lookUpVertexbyName
if (iter == <vector>.end() {
    // abort or do what ever you want
}

To use the value you have to dereference the iterator. DON'T derefence the end-iterator, it will lead you to neverland -> undefined behavior.

std::string test = *iter;