Question

I’ve been going over and refactoring some code. I ended up changing a function from:

void setPerspective(float nearP = 0.1f, float farP = 1000.0f);

to

void setPerspective(float near = 0.1f, float far = 1000.0f);

and started getting a lot of strange 'missing ;' and 'missing )' errors.

It seems that near and far are #defined in windef.h. Fair enough; I’ll avoid using them.

But then I noticed in another header file:

void setPerspective(float fov, float aspect, float near, float far);

Yet I get no trouble. Both of these header files have the same #includes…

Any idea why I’m getting issues in one, but not another? It doesn’t seem to be the default parameters. Is it some arbitrary ordering of the #includes that might be causing issues with one header file and not another?

Answer 1

The tokens near and far are probably defined to be null in an empty #define like this

#define near
#define far

so the pre-processor will replace them with null – they disappear prior to the compiler processing the source.

The first function declaration includes the default assignment to the parameters

void setPerspective(float nearP = 0.1f, float farP = 1000.0f);

The compiler correctly interprets nearP and farP as the parameter name and float as the type. When you change nearP to near and farP to far the pre-processor replaces them with null and you have an assignment to the float type… and the compiler throws a fit… this is what the compiler sees:

void setPerspective(float  = 0.1f, float  = 1000.0f);

In the second header file the parameters in the function prototype don’t have default assignment, and the compiler sees the parameters are float and doesn’t see near and far because they are null… so instead of this

void setPerspective(float fov, float aspect, float near, float far);

the compiler sees this

void setPerspective(float fov, float aspect, float , float );

which is a perfectly legal function prototype (you don’t have to give the parameters names).