How to use find_if to find a matching object of a class? (Or any other way to achieve the result)

Question

I'm trying to traverse through a vector of "Stimulus" class objects. And if the properties of the object match the criteria, I want that Stimulus object returned.

std::vector<Stimulus> BS_stimulus_list;

bool StimulusCollection::isNextPoint(Stimulus it){
if(it.GetPointDeg()=="(Some json value)" & it.GetEye()==currentEye){
    return true;
}
else{
    return false;
}

void StimulusCollection::NextBSStimulus(char e){
currentEye = e;
if (currentEye=='L'){
    vector<Stimulus>::iterator idx = find_if(BS_stimulus_list.begin(), BS_stimulus_list.end(),isNextPoint);
}

The code above gives me a compile error : must use '.' or '->' to call pointer-to-member function in..... What am I doing wrong? Or what should I do differently to avoid this altogether?

Is `isNextPoint` a static or non static function? – NathanOliver Sep 05 '18 at 14:44 — NathanOliver, Sep 05 '18 at 14:44

score 1 · Answer 1 · answered Sep 05 '18 at 14:45

Assuming that isNextPoint is marked static, you need to explicitly qualify it:

find_if(BS_stimulus_list.begin(), 
        BS_stimulus_list.end(), 
        StimulusCollection::isNextPoint)

If it's not static you can use a lambda expression in order to bind the invocation of isNextPoint to a particular instance of StimulusCollection.

dan · Accepted Answer · 2018-09-07T10:57:02.220

1

you have to specify the instance, either by using a lambda (see below) or std::bind

void StimulusCollection::NextBSStimulus(char e) {
    currentEye = e;
    if (currentEye=='L'){
        vector<Stimulus>::iterator idx = find_if(
            BS_stimulus_list.begin(), 
            BS_stimulus_list.end(),
            [this](const auto& stimulus) { return isNextPoint(stimulus); });
    }
}

(for C++14, change const auto& to const Stimulus& for older versions)

edited Sep 07 '18 at 10:57

answered Sep 05 '18 at 14:51

dan

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1
3

Thanks, this works with a little modification. [this](const auto& stimulus) { return isNextPoint(stimulus); }); is changed to [this](const Stimulus& stimulus) { return isNextPoint(stimulus); }); – ni5arg Sep 05 '18 at 15:08

How to use find_if to find a matching object of a class? (Or any other way to achieve the result)

2 Answers2