C example code to list all network interfaces and check whether they are wireless or not. Linux only. Tested on Ubuntu 10.04 and 12.04, but should be compatible with pretty much everything out there.

is_wireless.c

#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <ifaddrs.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/wireless.h>


int check_wireless(const char* ifname, char* protocol) {
  int sock = -1;
  struct iwreq pwrq;
  memset(&pwrq, 0, sizeof(pwrq));
  strncpy(pwrq.ifr_name, ifname, IFNAMSIZ);

  if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
    perror("socket");
    return 0;
  }

  if (ioctl(sock, SIOCGIWNAME, &pwrq) != -1) {
    if (protocol) strncpy(protocol, pwrq.u.name, IFNAMSIZ);
    close(sock);
    return 1;
  }

  close(sock);
  return 0;
}


int main(int argc, char const *argv[]) {
  struct ifaddrs *ifaddr, *ifa;

  if (getifaddrs(&ifaddr) == -1) {
    perror("getifaddrs");
    return -1;
  }

  /* Walk through linked list, maintaining head pointer so we
     can free list later */
  for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
    char protocol[IFNAMSIZ]  = {0};

    if (ifa->ifa_addr == NULL ||
        ifa->ifa_addr->sa_family != AF_PACKET) continue;

    if (check_wireless(ifa->ifa_name, protocol)) {
      printf("interface %s is wireless: %s\n", ifa->ifa_name, protocol);
    } else {
      printf("interface %s is not wireless\n", ifa->ifa_name);
    }
  }

  freeifaddrs(ifaddr);
  return 0;
}