How to Fix 'passing const xxx as 'this' argument of member function discards qualifiers' Error in C ?

Error Solving: Handling 'Passing Const Argument as 'This' Argument'

When encountering the error "passing const xxx as 'this' argument of member function discards qualifiers," it indicates that a non-const member function is being called on a const object. In this case, the issue arises when accessing getId() and getName() methods of StudentT objects stored within a std::set.

Problem Analysis

The objects in the std::set are stored as const StudentT. When calling getId() and getName() on the iterator dereference (*itr), the compiler detects a mismatch. The member functions are non-const, but the object being accessed is const.

Solution

To resolve this issue, the member functions getId() and getName() should be declared as const methods:

int getId() const {
    return id;
}
string getName() const {
    return name;
}

By declaring them as const methods, it guarantees that they will not modify the StudentT object, making it safe to call them on const objects.

Additional Consideration

The operator< should also be declared as a const method, as it is called on const StudentT objects when performing set operations:

inline bool operator< (const StudentT & s1, const StudentT & s2) {
    return s1.getId() < s2.getId();
}

By declaring it as const, it ensures that the operator does not modify the objects being compared.

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