Question

I have casting problem with structures in my C++ code. I use C-style casting. But if i try to cast using alternative name (created using typedef) i have an error. Please, look at my code.

class T
{
public:
    typedef struct kIdS* kIdN;
    typedef struct kIdS {
        int* a;
        double* b;
    }  kIdR;

    typedef struct tIdS {
        int* a;
        double* b;
        float* c;
    }  tIdR;

    int a;
    double b;
    float c;

    void F()
    {
        a = 0; 
        b = 0; 
        c = 0;
        struct kIdS A = {&a, &b};
        struct tIdS B = {&a, &b, &c};
        struct kIdS* knv[] = {&A, (struct kIdS*)&B};
        struct kIdS* knv1[] = {&A, (kIdN)&B}; //error
    }
};

The error is:

error C2440: 'initializing' : cannot convert from 'T::kIdN' to 'T::kIdS *'
    Types pointed to are unrelated; conversion requires reinterpret_cast, 
    C-style cast or function-style cast

Why i can not use alternative name? How i can solve this problem using alternative name created by typedef?

Answer 1

The reason for your error is in first typedef struct kIdS* kIdN you have no struct in your class that named kIdS, so C++ compiler think that you are talking about a global struct kIdS and then typedef that global struct to kIdN and in line struct kIdS* knv1[] = {&A, (kIdN)&B}; error is obvious, global struct kIdS* can’t be used instead of T::kIdS*, but I have a question from you, why you use struct X while you can simply say X??