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c++calloc

I'm getting "invalid conversion from `void*` to `std::complex<double>*"

I have the following code below,

std::complex<double>** x;
x = calloc(10,sizeof(complex <double> *));

This code failed to compile with the following error message.

error: invalid conversion from 'void*' to 'std::complex<double>*' [-fpermissive]

How can I successfully compile? Why does this code fail to compile?

Solution

  • In C++, void * doesn't automatically cast to other pointers (unlike in C). So if you use malloc and the family in C++, you need to cast the result yourself.

    However, you should note that malloc doesn't understand C++'s constructors. So if you want to allocate a C++ object (not a C struct for example, or more precisely a POD), you should use new (and delete/delete[] correspondingly) which correctly takes care of constructors and destructors.

    Alternatively, you can use one of the many structures provided by the standard library, such as std::vector.