Question

Say I have this piece of code.

#include <string>

int main()
{
    std::string(0);
    return 0;
}

Writing std::string(0) results in std::basic_string<char>::basic_string(const char*) being called, with 0 as the argument to this constructor, which tries to treat the argument as a pointer to a C-string.

Running this code obviously results in a std::logic_error being thrown. But my question is this : why both GCC and MSVC 8.0 don’t emit any warnings? I’d expect to see something along the lines of “Making pointer from an integer without a cast”.

Answer 1

0 is an integer constant expression with value 0, so it is a null pointer constant. Using a 0-valued constant as a null pointer is not a cast.

C++11 introduces nullptr (and nullptr_t), but the treatment of 0 as a null pointer is unlikely to change in the near future as large amounts of code depends on it.