compile time error or runtime error?

George2 · 05-04-2008, 03:41 AM

Hello everyone,

Could anyone let me know why compiler can not make runtime error report in the following code, other than throw cast exception during runtime?

Code:

    static void Main()
    {
        int i = 100;
        object b = i;
        long l = (long)b; // why compiler can not make type check here?

        return;
    }

thanks in advance,
George

**laserlight** · 05-04-2008, 03:56 AM

Did you mean to say: "why compiler can not make compile time error report in the following code"?

Magos · 05-04-2008, 05:21 AM

Because b is an "object" which can be a "long" (which is valid cast) but also something else (which might be invalid cast). The compiler does not know, and far from all cases are as easy to detect as the one you show.

George2 · 05-07-2008, 07:08 AM

Thanks laserlight and Magos,

Are there any documents about why type cast/conversion are checked by C# compiler? :-)

Quote:

Originally Posted by Magos

Because b is an "object" which can be a "long" (which is valid cast) but also something else (which might be invalid cast). The compiler does not know, and far from all cases are as easy to detect as the one you show.

regards,
George

05-04-2008, 03:41 AM	#1
George2 Registered User Join Date: May 2006 Posts: 1,579	compile time error or runtime error? Hello everyone, Could anyone let me know why compiler can not make runtime error report in the following code, other than throw cast exception during runtime? Code: static void Main() { int i = 100; object b = i; long l = (long)b; // why compiler can not make type check here? return; } thanks in advance, George
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05-04-2008, 03:56 AM	#2
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 11,372	Did you mean to say: "why compiler can not make compile time error report in the following code"? __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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05-04-2008, 05:21 AM	#3
Magos Confused Join Date: Sep 2001 Location: Sweden Posts: 3,125	Because b is an "object" which can be a "long" (which is valid cast) but also something else (which might be invalid cast). The compiler does not know, and far from all cases are as easy to detect as the one you show. __________________ MagosX.com Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.
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