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What does template <unsigned int N> mean?

Hi ! Are non-type template parameters and constants same ? Do the following code work because template parameter cannot be modified ? If can be modified, the compiler should have thrown error while declaring array "a[T]". Is my understanding correct ?

template < int T > 
void foo() {  
  int a[T] ;  
}  

int main( int argc, const char* argv[] ) {  
  foo <3> () ;  
  system("pause") ;  
  return 0 ;  
}
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Mahesh
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  • @ybungalobill Thanks for editing the code part.The way I did was - started with 
     tag and ended with 
    . And for each end of line, I have given 1 space. While in preview, it shows correctly. But after posting, it is changing? It would be helpful for further posts if you can say me the way you edited ?
    
        – Mahesh
                Dec 27 '10 at 21:08
    
    

    
                    
                
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        @marcog The link was very helpful. Thanks.
        – Mahesh
                Dec 27 '10 at 21:08
    
    

    
                    
                
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        @marcog: I agree. Especially Johannes' answer is very exhaustive.
        – sbi
                Dec 27 '10 at 21:08
    
    

    
                    
                
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        You can see it [here](http://stackoverflow.com/revisions/35794e13-1e4d-45f4-9206-71505d9aa94d/view-source). You begin each line of the code with 4 spaces, or just use the code button on the toolbar: {}
        – Yakov Galka
                Dec 27 '10 at 21:11
    
    

    
                    
                
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Yeah, kind of. Thing is every time you instantiate a template the compiler will generate specific code for that specific type parametrization. So for instance, in your example if you have foo<3> and foo<5> the compiler will generate code for two separate functions one where T=3 and one where T=5


So yeah, it works because T can't change, the mechanism why it works is slightly more complex though...

        
        

            

                

                
                

                    
                    
                        


    
    
        
    
    

        Dr G
        
    
            
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Yes, non-template parameters have to be constant expressions.

        
        

            

                

                
                

                    
                    
                        


    
    
        
    
    

        Edward Strange
        
    
            
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