C# null coalescing operator equivalent for c++

I just found this: The ?? operator aka the Null Coalescing Operator

You also have it in C/C++ as a GNU extension using the ?: operator :

string pageTitle = getTitle() ?: "Default Title";

There isn't a way to do this by default in C++, but you could write one:

in C# the ?? operator is defined as

a ?? b === (a != null ? a : b)

So, the C++ method would look like

Coalesce(a, b) // put your own types in, or make a template
{
    return a != null ? a : b;
}

Using templates and C++11 lambdas. The first argument (left-hand side) is only evaluated once. The second argument (right-hand side) is only evaluated if the first is false (note that 'if' and '?' statically cast the provided expression to bool, and that pointers have 'explicit operator bool() const' that is equalivent to '!= nullptr')

template<typename TValue, typename TSpareEvaluator>
TValue
coalesce(TValue mainValue, TSpareEvaluator evaluateSpare) {

    return mainValue ? mainValue : evaluateSpare();
}

Example of use

void * const      nonZeroPtr = reinterpret_cast<void *>(0xF);
void * const otherNonZeroPtr = reinterpret_cast<void *>(0xA);

std::cout << coalesce(nonZeroPtr, [&] () { std::cout << "Never called"; return otherNonZeroPtr; }) << "\n";

Will just print '0xf' in the console. Having to write a lambda for the rhs is a little bit of boilerplate

[&] () { return <rhs>; }

but it's the best that one can do if one lacks support by the language syntax.