count_variadic_parameters.c

#include <stddef.h>
#include <stdbool.h>
#include <assert.h>

/*! \brief transfer the variadic parameters to string literal
 * */
#define argsstr(...) (#__VA_ARGS__)

/*! \brief check the validation of variadic parameters
 *  \param dummy required before variadic parameters
 *  \param ... the variadic parameters
 * */
int check(int dummy, ...) {
    return dummy;
}

size_t count_args_by_str(const char * args) {
    bool in_str = false;
    bool in_char = false;
    size_t count = 0;

    if (NULL == args || '\0' == *args) {
        return count;
    }

    while('\0' != *args) {
        if ('\"' == *args && '\\' != *(args-1)) {
            in_str = !in_str;
        }
        if ('\'' == *args && '\\' != *(args-1)) {
            in_char = !in_char;
        }
        
        if (*args == ',' && !in_str && !in_char) {
            count++;
        }
        args++;
    }

    return count + 1;
}

#define count_args(...) (check(0, ## __VA_ARGS__), \
        count_args_by_str(argsstr(__VA_ARGS__)))

int main(int argc, char * argv[]) {
    assert(0 == count_args());

    assert(1 == count_args(1));
    assert(1 == count_args(""));
    assert(1 == count_args('\''));

    assert(2 == count_args('\'', "Hello, World!"));

    assert(3 == count_args(-1.1, ',', ",,,"));

    // invalid call like count_args(3, ), count_args(,) and count_args(, 3) will
    // invoke compile error
    return 0;
}