MessageBox Value Passing Error

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Hi all,

I'm new to VC++, and cannot figure out why my MessageBox call here is error'ing out when executed:

	void center(char *s)
	{
	 int len;
	
	 len = (strlen(s));

	 MessageBox::Show(len);
	}

The resulting build would produce:

1>c:\users\test\documents\visual studio 2010\projects\test\test\Form1.h(90): warning C4068: unknown pragma
1>c:\users\test\documents\visual studio 2010\projects\test\test\Form1.h(116): warning C4101: 'found' : unreferenced local variable
1>c:\users\test\documents\visual studio 2010\projects\test\test\Form1.h(152): error C2665: 'System::Windows::Forms::MessageBox::Show' : none of the 21 overloads could convert all the argument types
1>          c:\program files\reference assemblies\microsoft\framework\.netframework\v4.0\system.windows.forms.dll: could be 'System::Windows::Forms::DialogResult System::Windows::Forms::MessageBox::Show(System::String ^)'
1>          while trying to match the argument list '(int)'

Thanks in advance

Posted 2-Apr-12 9:31am

stoneferry_tiger

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Sergey Alexandrovich Kryukov 2-Apr-12 18:01pm

It looks like C++/CLI and .NET, mixed mode with native Win32. Tag it.
--SA

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Sergey Alexandrovich Kryukov · Answer 1 · 2012-04-02T12:15:00

The error message clearly shows the problem: it expects the string, not integer. And it should be System::String, not char*. The solution of the problem is: use MessageBox::Show(len.ToString()); however, it's generally bad to mix native C++ code with .NET C++/CLI without special need for it.

One nice discipline for mixed-mode code I would advice is: strictly classify all files into 1) pure managed C++/CLI code; 2) pure unmanaged C++ code; 3) managed C++/CLI code wrapping unmanaged C++ types in managed "ref" classes or structures; 4) unmanaged C++ code wrapping managed "ref" types in unmanaged classes or structures. In most mixed-mode projects, either class #3 or #4 will be used, not both of them.

—SA