Query on c++ iterator tag -

i going through code snippet

template <class raiter> void alg(raiter, raiter, std::random_access_iterator_tag) {     std::cout << "alg() called random-access iterator\n"; }

for first time, seeing data types in function parameter section (std::random_access_iterator_tag). used seeing

[std::random_access_iterator_tag rand_iter;]

this sort of representation allowed in templates not in non-templated functions.

two questions:

1) why data type name mentioned no variable of mentioned?

2) why allowed templated functions not non-templated functions?

actually that's not related templates @ all.

it's unnamed parameter , it's legal when:

basically can respect signature without having named argument @ costs, eg:

float foo(float, int, float);  int main() {   float x = foo(10.0f, 5, 20.0f);   return 0; }  float foo(float a, int, float b) {   return a+b; }

this can useful in specific circumstances, think pure virtual methods or forward declaration of methods.

in specific case helps suppress unused parameter warning, example:

float foo(float a, int z, float b) {   return a+b; }

this yields warning -wunused-parameter won't if explicitly state won't use removing name.

Panthy J