Is there an equivalent in C for C++ templates?

Yes, there is. You can use type-generic expression in C11:

#include <stdio.h>

void foo_char_ptr(int a, char *b) {
  printf("Called int, char*.\n");
}

void foo_int(int a, int b) {
  printf("Called int, int.\n");
}

#define foo(a, b) _Generic((b), char*: foo_char_ptr, int: foo_int)(a, b)

int main() {
  foo(1, 1);
  foo(1, "foo");
}

// Output:
// Called int, int.
// Called int, char*.

I think the closest you can get in C to templates is some ugly macro code. For example, to define a simple function that returns twice its argument:

#define MAKE_DOUBLER(T)  \
    T doubler_##T(T x) { \
        return 2 * x;    \
    }

MAKE_DOUBLER(int)
MAKE_DOUBLER(float)

Note that since C doesn't have function overloading, you have to play tricks with the name of the function (the above makes both doubler_int and doubler_float, and you'll have to call them that way).

printf("%d\n", doubler_int(5));
printf("%f\n", doubler_float(12.3));