Why Can't I Pass a Temporary Object as a Non-Const Reference in C ?

Passing a Temporary Object as Reference

When attempting to pass a temporary object as a non-const reference, such as in the following code:

void ProcessFoo(Foo& foo)
{
}

int main()
{
    ProcessFoo(Foo(42)); // Error: Can't pass temporary object as reference
}

compilers like g and clang raise an error. This occurs because, by design, C restricts passing temporaries to const references, value parameters, or rvalue references.

The rationale behind this restriction is that functions receiving non-const reference parameters intend to modify those parameters and return them to the caller. Passing a temporary in this scenario is considered nonsensical and likely indicative of an error.

To resolve this issue, several workarounds are available:

1. Using a Temporary Variable

Create a temporary variable and pass it to the function as an argument:

Foo foo42(42);
ProcessFoo(foo42);

2. Declaring the Function with a const Reference Parameter

Modify the function declaration to accept a const reference:

void ProcessFoo(const Foo& foo)
{
}

3. Passing by Value

Allow the function to accept the object by value:

void ProcessFoo(Foo foo)
{
}

Visual Studio allows this original code due to a less restrictive compiler implementation.

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