CODEWITHSUNDEEP
c++
liil
liil

Reputation: 37

I need help writing a function that checks the data type of another variable

Hi i'm having trouble making a function that checks the data type of a variable and checks it to make sure if a data type is similar to it in C++. Here's my code so far: 

#include <iostream>
#include <typeinfo>
using namespace std;




int main() {

    int typeCheck(string words, string typeWanted);

    //make number assurance function        .

        string word;
        cin >> word;

        typeCheck(word, "string");

}

int typeCheck(string words, string typeWanted) {
    if (typeid(words).name() != typeid(typeWanted).name()) {
        cin.clear();
        cin.ignore();
        return 0;
    }
    else if (typeid(words).name()== typeid(typeWanted).name())
        cout << "All good";
}

When I run the code it keeps saying the same output which is: All good even if I put a string or an int when its not the correct one. Instead of saying this I want it to clear the buffer and ignore it. Can anyone help me with this problem? Thanks in advance!

Upvotes: 3

Views: 76

Answers (2)

user10957435
user10957435

Reputation:

C++ is a statically typed language, meaning that the type is known at compile time. It will never be known only at run time.

What that means is that in your example:

int typeCheck(string words, string typeWanted);

both words and typeWanted will always be strings. If it is ever not a string, it will fail to compile. Thus, using typeid() in this situation is somewhat pointless. Your if statement will always be false, and your else-if statement will always be true.

Instead, you would want to use typeid() when you don't know they will be the same type, like in some sort of template situation:

template <class WordsType, class TypeWantedType>
int typeCheck(WordsType words, TypeWantedType typeWanted);

Here, a typeid() comparison makes more sense, because you don't really know if words and typeWanted are both strings.

You could do something like this instead:

template <class WordsType>
int typeCheck(WordsType words, string typeWanted) {
    if (typeid(words).name() != typeWanted) {
        //...
    }
    // ...
}

This would compare an unknown type to a wanted type.

Finally, there is another option, @RSahu's option from the comments:

if(words == typeWanted) {
//...
}

This will compare the input the user gave to the string "string".

It's unclear to me what you want to do exactly, so I can't recommend which one you should use, but at least now you have a couple of options.

Upvotes: 3

UnReal G
UnReal G

Reputation: 136

It is because you are converting the type to string eaither way so it will allways trigger as correct as long as it is a string in the function input.

I would recommend that you use a template type so that whatever you enter into the TypeCheck() function will retain its type.

Upvotes: 2

Related Questions