Compiler Error C2057

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The latest version of this topic can be found at Compiler Error C2057.

expected constant expression

The context requires a constant expression, an expression whose value is known at compile time.

The compiler must know the size of a type at compile time in order to allocate space for an instance of that type.

The following sample generates C2057 and shows how to fix it:

// C2057.cpp  
int i;  
int b[i];   // C2057 - value of i is unknown at compile time  
int main() {  
   const int i = 8;  
   int b[i]; // OK - value of i is fixed and known to compiler  
}  

C has more restrictive rules for constant expressions. The following sample generates C2057 and shows how to fix it:

// C2057b.c  
#define ArraySize1 10  
int main() {   
   const int ArraySize2 = 10;   
   int h[ArraySize2];   // C2057 - C does not allow variables here  
   int h[ArraySize1];   // OK - uses preprocessor constant  
}