ios:crash in 64 bit device

问题:

Can someone explain why my app crashes with the following error:

EXC_BAD_ACCESS(Code = 1, address= ...)

This crash occurs only in 64 bit devices. I am not able to figure it out.

  - (NSString *)getIPAddress
    {
        NSString *address = nil;
        struct ifaddrs *interfaces = NULL;
        struct ifaddrs *temp_addr = NULL;
        int success = 0;

        // retrieve the current interfaces - returns 0 on success
        success = getifaddrs(&interfaces);
        if (success == 0)
        {
            // Loop through linked list of interfaces
            temp_addr = interfaces;
            while(temp_addr != NULL)
            {
                if(temp_addr->ifa_addr->sa_family == AF_INET)// crashes here
                {
                    // Check if interface is en0 which is the wifi connection on the iPhone
                    if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"])
                    {
                        // Get NSString from C String
                        address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)]; // crash also here
                    }
                }
                temp_addr = temp_addr->ifa_next;
            }
        }
        // Free memory
        freeifaddrs(interfaces);
        return address;
    }

Thanks!

回答1:

According to the documentation:

The ifa_addr field references either the address of the interface or the link level address of the interface, if one exists, otherwise it is NULL. (The sa_family field of the ifa_addr field should be consulted to determine the format of the ifa_addr address.)

It is likely there is an interface on your 64-bit device that does not have the ifa_addr field populated.

To fix your problem, check for a NULL ifa_addr. I also recommend breaking out of the loop since you are finished once you find en0.

...
while(temp_addr != NULL)
{
    if(temp_addr->ifa_addr != NULL && temp_addr->ifa_addr->sa_family == AF_INET)
    {
        // Check if interface is en0 which is the wifi connection on the iPhone
        if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"])
        {
            // Get NSString from C String
            address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
            break;
        }
    }
    temp_addr = temp_addr->ifa_next;
}
...