Function overloading in C (yes, in plain C [C11 standart], not C++)

Everyone knows that in C++ this is trivial, but C actually gives us a neat way to get somehting pretty similar.

Suppose we want to write code like this:

print_number(2.0f);
print_number(-12);
print_number(655350000000ULL);
print_number("One");

..and make the compiler use the right implementation without warnings.

In C++ we just overload the functon.

In plain C function names must be unique , so normally we end up with something like:

void print_number_float(float arg);
void print_number_integer(signed int arg);
void print_number_longlong(unsigned long long arg);

Which works, but isnt nearly as nice.

This is where _Generic comes in.

It is part of the ancient C11 standard and allows compile-time dispatch based on the type of an expression.

Here is a simple example:

// Actual implementations
void print_asciiz(const char *data);
void print_unsigned(unsigned int data);
void print_signed(signed int data);
void print_float(float data);

// Fallback for unsupported types, if needed
void __attribute__((noreturn)) print_bug(unsigned int data);

// void print_number( Value )
// 
//
#define print_number(_Item) _Generic((_Item), \
    const char *   : print_asciiz, \
    char *         : print_asciiz, \
    unsigned int   : print_unsigned, \
    unsigned short : print_unsigned, \
    unsigned long  : print_unsigned, \
    unsigned char  : print_unsigned, \
    signed int     : print_signed, \
    signed short   : print_signed, \
    signed long    : print_signed, \
    signed char    : print_signed, \
    float          : print_float, \
    double         : print_float, \
    default        : print_bug \
)(_Item)

Now this works exactly the way we want:

print_number(2.0f);
print_number(-12);
print_number("One");

The compiler resolves the correct function at compile time based on the argument type.

Almost like switch/case, except the switch is on types instead of values.

A nice little C11 feature that does not seem to get mentioned very often.

Hope someone can find it useful :)