Accessing member functions of sockaddr_in

Stack Overflow · 01-27-2005, 12:32 PM

Hello,

I am working on a small project in Linux that allows communication to and from a server. So far I have my concept in mind, and source code close to flawless. Though, I have a small problem. To reduce the size of code used in main, I created a structure to allow the handles of clients, sockets, and other information store in different areas. Though, to make my job easier, I want to pass the address of a sockaddr_in and access its members inside a function.

Though, when I do, it gives an error as the following: "request for member 'sin_family' in something not a structure or union"

Here is a code sample:

Code:

void setInfo(struct sockaddr_in *sock) {
    memset(sock, 0, sizeof(*sock));
    *(sock.sin_family) = AF_INET;
    *(sock.sin_port) = htons(port);
    *(sock.sin_addr.s_addr) = INADDR_ANY;
}

int main() {
    struct sockaddr_in server;

    setInfo(&server);

    return 0;
}

Compiled with GCC 3.4.3 | Slackware 10.0

At this moment, I'm clueless of why it won't accept the indirection (*) operator. Any help would be appreciated.

- Stack Overflow

Stack Overflow · 01-27-2005, 01:18 PM

Scratch that,

Just got word that I shouldn't dereference sock.sin_family because sock.sin_family does not exist. Rather I should dereference sock:

Code:

void setInfo(struct sockaddr_in *sock) {
    memset(sock, 0, sizeof(*sock));
    *(sock).sin_family = AF_INET;
    *(sock).sin_port = htons(port);
    *(sock).sin_addr.s_addr = INADDR_ANY;
}

int main() {
    struct sockaddr_in server;

    setInfo(&server);

    return 0;
}

Alternatively, I could use the struct pointer syntax (->). Though, is that legal in this case?

- Stack Overflow

edugarcia · 01-27-2005, 03:17 PM

Yeah, it's legal. Why shouldn't be, there's no excepcion here, I guess

p->field == (*p).field

curlious · 01-27-2005, 08:05 PM

Just a comment I like your seperation into routines. When I had time I was exploring the idea of wrapping different functionality in C++ but school started and I just did a very linear walk through. Now my interests have wanderd (Eiffel) but nice looking code.
What type of networking app are you creating. Have you explored threads yet?

Stack Overflow · 01-28-2005, 11:00 AM

Well,

I'm just trying to make a test echo server. Though, I am adding a hash table to store and organize all the clients that connect. So I can look them up, remove them, add them, and other fun stuff. It's just to test my C ability. I have not checked out threads as of yet, though maybe I will.

I've been working on this project for some time now, though now I am developing it under the Linux environment. I've spent a while allowing executable options. And also able to read in a configuration file and parse it. Though, I spent yesterday cleaning up all the compiler warnings and errors for GCC 3.4.3 since it's a bit more picky than usual, esp. with the -g, -O2, -Wall, -pedantic, -ansi, and -std=c89 flags. Though, I managed to make the build perfectly clean.

Right now, I need to figure out why all connections never make it through to the server. No matter how many clients I write.

- Stack Overflow

Sebastiani · 01-28-2005, 12:52 PM

>> Right now, I need to figure out why all connections never make it through to the server.

did you remember to bind() and listen()? or, do you have a firewall running?

Stack Overflow · 01-28-2005, 12:58 PM

Yes,

I remembered to bind() and listen(), though I found the problem. I had a loop that ran through all the waiting clients to process, but my loop was wrong. Thus sending my server into an infinte loop. Once I fixed it, I was able to connect and send data to my server.

P.S. This is a multi-client server. So it takes more handling and care.

Now I am working on sending data back to the client. This is going to be fun!

- Stack Overflow

curlious · 01-28-2005, 07:36 PM

It sounds like you will want to use select which takes a set of file discriptors in this case socket discriptors then if the discriptor is flagged to be watched it returns a subset based on the active sockets. You would then be able to put these into whatever data structure you wish. I am curious if you have implemented your hash table and how you monitor for activity otherwise.

Stack Overflow · 01-29-2005, 11:26 AM

Ah,

Yes. I so far am using select(). Though, I'm using two instances. One to look for incoming connections, and the other, to read in the local input stream [stdin]. Through thorough testing, I succeeded at accomplishing the both desired effects.

Now, all is running well. I am working on a client, so I can send and receive information in a nice fashion.

My hashing function just stores the clients IP address and Port they connect with, dynamically. Each client's node includes a name and a few other miscellanous client storage variables. I'm going to try and make a chat server that takes in x amount of people, etc... So far my server is 75% complete, and my client 50% complete.

- Stack Overflow

01-27-2005, 12:32 PM	#1
Stack Overflow C Programmer Join Date: Apr 2004 Posts: 477	Accessing member functions of sockaddr_in Hello, I am working on a small project in Linux that allows communication to and from a server. So far I have my concept in mind, and source code close to flawless. Though, I have a small problem. To reduce the size of code used in main, I created a structure to allow the handles of clients, sockets, and other information store in different areas. Though, to make my job easier, I want to pass the address of a sockaddr_in and access its members inside a function. Though, when I do, it gives an error as the following: "request for member 'sin_family' in something not a structure or union" Here is a code sample: Code: void setInfo(struct sockaddr_in sock) { memset(sock, 0, sizeof(sock)); (sock.sin_family) = AF_INET; (sock.sin_port) = htons(port); (sock.sin_addr.s_addr) = INADDR_ANY; } int main() { struct sockaddr_in server; setInfo(&server); return 0; } Compiled with GCC 3.4.3 \| Slackware 10.0 At this moment, I'm clueless of why it won't accept the indirection* (*) operator. Any help would be appreciated. - Stack Overflow __________________ Segmentation Fault: I am an error in which a running program attempts to access memory not allocated to it and core dumps with a segmentation violation error. This is often caused by improper usage of pointers, attempts to access a non-existent or read-only physical memory address, re-use of memory if freed within the same scope, de-referencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.
Stack Overflow is offline

01-27-2005, 01:18 PM	#2
Stack Overflow C Programmer Join Date: Apr 2004 Posts: 477	Scratch that, Just got word that I shouldn't dereference sock.sin_family because sock.sin_family does not exist. Rather I should dereference sock: Code: void setInfo(struct sockaddr_in sock) { memset(sock, 0, sizeof(sock)); (sock).sin_family = AF_INET; (sock).sin_port = htons(port); *(sock).sin_addr.s_addr = INADDR_ANY; } int main() { struct sockaddr_in server; setInfo(&server); return 0; } Alternatively, I could use the struct pointer syntax (->). Though, is that legal in this case? - Stack Overflow __________________ Segmentation Fault: I am an error in which a running program attempts to access memory not allocated to it and core dumps with a segmentation violation error. This is often caused by improper usage of pointers, attempts to access a non-existent or read-only physical memory address, re-use of memory if freed within the same scope, de-referencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.
Stack Overflow is offline

01-27-2005, 03:17 PM	#3
edugarcia Registered User Join Date: Sep 2004 Posts: 13	Yeah, it's legal. Why shouldn't be, there's no excepcion here, I guess p->field == (*p).field
edugarcia is offline

01-27-2005, 08:05 PM	#4
curlious Registered User Join Date: Jul 2003 Posts: 450	Just a comment I like your seperation into routines. When I had time I was exploring the idea of wrapping different functionality in C++ but school started and I just did a very linear walk through. Now my interests have wanderd (Eiffel) but nice looking code. What type of networking app are you creating. Have you explored threads yet?
curlious is offline

01-28-2005, 11:00 AM	#5
Stack Overflow C Programmer Join Date: Apr 2004 Posts: 477	Well, I'm just trying to make a test echo server. Though, I am adding a hash table to store and organize all the clients that connect. So I can look them up, remove them, add them, and other fun stuff. It's just to test my C ability. I have not checked out threads as of yet, though maybe I will. I've been working on this project for some time now, though now I am developing it under the Linux environment. I've spent a while allowing executable options. And also able to read in a configuration file and parse it. Though, I spent yesterday cleaning up all the compiler warnings and errors for GCC 3.4.3 since it's a bit more picky than usual, esp. with the -g, -O2, -Wall, -pedantic, -ansi, and -std=c89 flags. Though, I managed to make the build perfectly clean. Right now, I need to figure out why all connections never make it through to the server. No matter how many clients I write. - Stack Overflow __________________ Segmentation Fault: I am an error in which a running program attempts to access memory not allocated to it and core dumps with a segmentation violation error. This is often caused by improper usage of pointers, attempts to access a non-existent or read-only physical memory address, re-use of memory if freed within the same scope, de-referencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.
Stack Overflow is offline

01-28-2005, 12:52 PM	#6
Sebastiani Guest Join Date: Aug 2001 Posts: 5,034	>> Right now, I need to figure out why all connections never make it through to the server. did you remember to bind() and listen()? or, do you have a firewall running?
Sebastiani is offline

01-28-2005, 12:58 PM	#7
Stack Overflow C Programmer Join Date: Apr 2004 Posts: 477	Yes, I remembered to bind() and listen(), though I found the problem. I had a loop that ran through all the waiting clients to process, but my loop was wrong. Thus sending my server into an infinte loop. Once I fixed it, I was able to connect and send data to my server. P.S. This is a multi-client server. So it takes more handling and care. Now I am working on sending data back to the client. This is going to be fun! - Stack Overflow __________________ Segmentation Fault: I am an error in which a running program attempts to access memory not allocated to it and core dumps with a segmentation violation error. This is often caused by improper usage of pointers, attempts to access a non-existent or read-only physical memory address, re-use of memory if freed within the same scope, de-referencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.
Stack Overflow is offline

01-28-2005, 07:36 PM	#8
curlious Registered User Join Date: Jul 2003 Posts: 450	It sounds like you will want to use select which takes a set of file discriptors in this case socket discriptors then if the discriptor is flagged to be watched it returns a subset based on the active sockets. You would then be able to put these into whatever data structure you wish. I am curious if you have implemented your hash table and how you monitor for activity otherwise.
curlious is offline

01-29-2005, 11:26 AM	#9
Stack Overflow C Programmer Join Date: Apr 2004 Posts: 477	Ah, Yes. I so far am using select(). Though, I'm using two instances. One to look for incoming connections, and the other, to read in the local input stream [stdin]. Through thorough testing, I succeeded at accomplishing the both desired effects. Now, all is running well. I am working on a client, so I can send and receive information in a nice fashion. My hashing function just stores the clients IP address and Port they connect with, dynamically. Each client's node includes a name and a few other miscellanous client storage variables. I'm going to try and make a chat server that takes in x amount of people, etc... So far my server is 75% complete, and my client 50% complete. - Stack Overflow __________________ Segmentation Fault: I am an error in which a running program attempts to access memory not allocated to it and core dumps with a segmentation violation error. This is often caused by improper usage of pointers, attempts to access a non-existent or read-only physical memory address, re-use of memory if freed within the same scope, de-referencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.
Stack Overflow is offline

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