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CppCompileTimeAssert

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(C++) assert at compile-time

There are two ways to do an assert at compile-time:

• Using a temporary array
• Using generic programming

One can also use BOOST_STATIC_ASSERT from the Boost C++ Librray.

Using a temporary array

The trick to this method is that an array cannot be of size zero. This method can also be used in C.

define STATIC_ASSERT(x) { const char temp[ (((x) == 0) ? 0 : 1) ] = {'\0'}; }


int main()
{
  STATIC_ASSERT( 1 + 1 == 2 );
  //The line below will give the following compile-time error:
  //  [C++ Error] : Array must have at least one element
  //STATIC_ASSERT( 1 + 2 == 2 );
}

Using generic programming

template <bool> struct CompileTimeAssert;
template<> struct CompileTimeAssert<true> {};
int main()
{
  CompileTimeAssert<((1+1)==2)> x;
  //The line below will give the following compile-time errors:
  //  [C++ Error] : Undefined structure 'CompileTimeAssert<0>'
  //  [C++ Error] : Size of 'y' is unknown or zero
  CompileTimeAssert<((1+2)==2)> y;
}

The trick is that the only existing struct CompileTimeAssert<> is CompileTimeAssert<true>. Therefore, the part between < > must be true!

'Compile time assert' links

• C

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