IOCTL error: to get the ssid through c program

rajashacks · 02-28-2011, 07:05 AM

dear all,

I was trying to get the ssid of WLAN through the following C program

/* Program to print the SSID of the current network */
/* getssid.c */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/wireless.h>

#define IW_INTERFACE "wlan0"

extern int errno;
struct iwreq wreq;

int main (void)
{
int sockfd;
char * id;

memset(&wreq, 0, sizeof(struct iwreq));
sprintf(wreq.ifr_name, IW_INTERFACE);

if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
fprintf(stderr, "Cannot open socket \n");
fprintf(stderr, "errno = %d \n", errno);
fprintf(stderr, "Error description is : %s\n",strerror(errno));
exit(1);
}
printf("Socket opened successfully \n");

id = malloc(IW_ESSID_MAX_SIZE+1);
wreq.u.essid.pointer = id;
if (ioctl(sockfd, SIOCGIWESSID, &wreq)) {
fprintf(stderr, "Get ESSID ioctl failed \n");
fprintf(stderr, "errno = %d \n", errno);
fprintf(stderr, "Error description : %s\n",strerror(errno));
exit(2);
}
printf("IOCTL Successfull\n");
printf("ESSID is %s\n", wreq.u.essid.pointer);
exit(0);
}

While trying to run I got the following error

Socket opened successfully
Get ESSID ioctl failed
errno = 7
Error description : Argument list too long

What is the cause of this error? any suggestions

timetraveler · 03-13-2011, 12:43 PM

Have a look at some wifi code that does this and is working.

mas94 · 04-29-2020, 07:57 AM

Quote:

Originally Posted by rajashacks

What is the cause of this error? any suggestions

I imagine, nine years on, you've either got this working or no longer care, but since Google brought me here looking for how to do this, perhaps this will be useful for someone in the future.

You need to set another field in the

Code:

wreq.u.essid

to the length of the buffer you've set

Code:

wreq.u.essid.pointer

to.

Complete working code:

Code:

/* Program to print the SSID of the current network */
/* getssid.c */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/wireless.h>

#define IW_INTERFACE "wlan0"

//extern int errno;

int main (void)
{
    struct iwreq wreq;
	memset(&wreq, 0, sizeof(struct iwreq));
	sprintf(wreq.ifr_name, IW_INTERFACE);

	int sockfd;
	if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
		fprintf(stderr, "Cannot open socket \n");
		fprintf(stderr, "errno = %d \n", errno);
		fprintf(stderr, "Error description is : %s\n",strerror(errno));
		exit(1);
	}
	printf("Socket opened successfully \n");

	char *id = malloc(IW_ESSID_MAX_SIZE+1);
	wreq.u.essid.pointer = id;
	wreq.u.essid.length = IW_ESSID_MAX_SIZE;
	if (ioctl(sockfd, SIOCGIWESSID, &wreq)) {
		fprintf(stderr, "Get ESSID ioctl failed \n");
		fprintf(stderr, "errno = %d \n", errno);
		fprintf(stderr, "Error description : %s\n",strerror(errno));
		exit(2);
	}
	printf("IOCTL Successfull\n");
	printf("ESSID is %s\n", (char*)(wreq.u.essid.pointer));
	exit(0);
}

Hope that helps someone in the future, as the original post did me :-)