Unhandled Exception - Access Violation Reading Location

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The code I have is compiling except for this error on this line. Unhandled Exception Access Violation Reading Location

C++

int s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);

Posted 15-Aug-11 17:10pm

Member 7766180

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4 solutions

Solution 1

what is the value of res? I suspect it's NULL or at least not pointing to a valid bit of memory.

Posted 15-Aug-11 17:27pm

User 583852

Updated 15-Aug-11 17:30pm

v2

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Member 7766180 15-Aug-11 23:39pm

I'm not sure but I tend to agree with you. How do I fix it?

struct addrinfo req, *res;
memset(&req, 0, sizeof(req));
req.ai_family = AF_UNSPEC;
req.ai_socktype = SOCK_STREAM;

if (getaddrinfo("192.168.168.40", "http", &req, &res) < 0)
{
perror("getaddrinfo");
return -1;
}

int s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
if (s < 0)
{
perror("socket");
return -1;
}
if (connect(s, res->ai_addr, res->ai_addrlen) < 0)
{
perror("connect");
closesocket(s);
return -1;
}

Solution 3

You should be setting the family to AF_INET

Do you know how to use the debugger to step through the program and inspect the value of variables?

Posted 15-Aug-11 18:25pm

User 583852

Comments

Member 7766180 16-Aug-11 11:27am

I switchet it to AF_INET. I know about step through but not how to get the varaible values.

Solution 4

Copy from help:

int WSAAPI getaddrinfo(
  __in          const char* nodename,
  __in          const char* servname,
  __in          const struct addrinfo* hints,
  __out         struct addrinfo** res
);

res 
A pointer to a linked list of one or more addrinfo structures that contains response information about the host.

That means res can contain additional informations if they exist. use the hints param thats a valid struct in your code.
regards.

Posted 16-Aug-11 5:45am

mbue

Comments

Member 7766180 16-Aug-11 14:54pm

I'll research and give it a try.

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User 583852 · Accepted Answer · 2011-08-15T17:48:00

Not sure but the doco says that getaddrinfo returns 0 for success. You should change your test to != 0 rather than < 0. It may be that all the error codes it can return are < 0 but it's still incorrect.

Also, res will be set to point to the head of a linked list of results. It may be that the first item in that list is not ai_family == AF_INET and some of the members you're accessing are not valid for the family of that item.

You could initialise res to NULL and then test for res != NULL to make sure getaddrinfo is actually populating the pointer.

from http://linux.die.net/man/3/getaddrinfo[^]

getaddrinfo(3) sets res to point to a dynamically-allocated linked list of addrinfo structures, linked by the ai_next member. There are several reasons why the linked list may have more than one addrinfo structure, including: if the network host is multi-homed; or if the same service is available from multiple socket protocols (one SOCK_STREAM address and another SOCK_DGRAM address, for example).

Unhandled Exception - Access Violation Reading Location

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