how to handle wrong value passing to constructor parameters?

Question

I have my class Stack

class Stack
{
public:
    Stack(unsigned int Size)
   {
    size = Size;
   }

private:
    unsigned int size;
    void* Block;
};

int _tmain(int argc, _TCHAR* argv[])
{
    Stack x(-1);
    return 0;
}

I want to make sure that even I pass negative value to the constructor argument that the object wont be constructed , but when I'm giving -1 value , it's accepting it and the variable size value is 4294967295 , which is the same -1 after removing the sing bit as far as I know ...

so how I shall handle this situation ? shall I throw exception ? or just make to take default value in case of wrong value ?

Depending on your compiler, you can at least get [compilation warnings](https://stackoverflow.com/questions/765709/why-compiler-is-not-giving-error-when-signed-value-is-assigned-to-unsigned-integ) for passing signed values as an unsigned parameter. As far as at runtime.... you might be SOL, because that behavior is [specified by the standard](https://stackoverflow.com/questions/2711522/what-happens-if-i-assign-a-negative-value-to-an-unsigned-variable) — Cory Kramer, Oct 01 '15 at 17:46
Use the "try catch" handler in your _tmain function and throw an exception in your class constructor. Check http://www.cplusplus.com/doc/tutorial/exceptions/ — ahPo, Oct 01 '15 at 17:47
@user2340218 Catch what? There will be no exception to catch. — Cory Kramer, Oct 01 '15 at 17:47
Do nothing and do not fight stupid programmers. A crash is a viable result in this case. — , Oct 01 '15 at 17:52

score 1 · Accepted Answer · answered Oct 01 '15 at 17:52

1

If you are using the Visual C++ compiler (MSVC), as a general rule, you may want to compile your code at /W4 (i.e. warning level 4), so the compiler speaks up more frequently, and helps identifying programmer's mistakes.

For example:

C:\Temp\CppTests>cl /EHsc /W4 /nologo test.cpp

warning C4245: 'argument' : conversion from 'int' to 'unsigned int',
signed/unsigned mismatch

EDIT

In addition, you may want to mark your constructor explicit, to avoid implicit bogus conversions from integers to instances of your Stack class.

answered Oct 01 '15 at 17:52

Mr.C64

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@AlphasSupremum with the explicit keyword – Borgleader Oct 01 '15 at 17:57
1

@AlphasSupremum: Just use the `explicit Stack(unsigned int Size)` syntax. Related [SO question here](http://stackoverflow.com/q/121162/1629821). – Mr.C64 Oct 01 '15 at 17:58

score 0 · Answer 2 · answered Oct 01 '15 at 17:51

I want to make sure that even I pass negative value to the constructor argument that the object wont be constructed

One way to do this is -Wsign-conversion -Werror

$ clang++ -Werror -Wsign-conversion -c stack.cpp
stack.cpp:18:13: error: implicit conversion changes signedness: 'int' to 'unsigned int' [-Werror,-Wsign-conversion]
    Stack x(-1);
          ~ ^~
1 error generated.


$ cat stack.cpp

class Stack
{
    public:
        Stack(unsigned int Size)
        {
            size = Size;
        }

    private:
        unsigned int size;
        void* Block;
};

typedef const char _TCHAR;
int _tmain(int argc, _TCHAR* argv[])
{
    Stack x(-1);
    return 0;
}

how to handle wrong value passing to constructor parameters?

2 Answers2