Error with accept();

I'm working my way through Beej's Tutorial, and have ran into a snag.

Code:

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new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);

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this portion of code is throwing some errors I'm not aware of.

invalid conversion from int* to socklen_t*
initializing argument 3 of int accept(int, sockaddr*, socklen_t*)

does anyone know why this is happening?

I think the third parameter should be sizeof(their_addr)...Probably why it's complaining about incorrect datatypes - what type is sin_size?

ok, i ran the same code as a c program instead of c++ and it worked.
does anyone know of a c++ version of beej's server.c?
i like c, but i'm more fluent with c++, and i feel i would learn more from that code.
do not get me wrong the c version has taught me a lot.

i've compiled the same code as C++ (gcc 3.3.5) and it worked. What compiler are you using?
what is sin_size type? should be socklen_t .
Nazca, no the 3rd arg to accept is a value-result argument, a pointer.

You are passing an int* as the third parameter, as the error message fairly obviously states it wants a socklen_t. It needs a pointer to be because it changes its value in teh accept to tell you how many bytes were written. wither make sin_size a socklen_t, as it wants, or cast it to a socklen_t* in the call.

I was using both VC++7 and GCC3.3.4 when I was having the problem.
I found another tutorial that is helping me with c++ and winsock, but i was still unable to get this code to work as c++.
here is the example code i'm using from beej's guide

Code:

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#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
 
#define MYPORT 3490 // the port users will be connecting to
 
#define BACKLOG 10 // how many pending connections queue will hold
 
main()
{
int sockfd, new_fd; // listen on sock_fd, new connection on new_fd
struct sockaddr_in my_addr; // my address information
struct sockaddr_in their_addr; // connector's address information
int sin_size;
 
sockfd = socket(AF_INET, SOCK_STREAM, 0); // do some error checking!
 
my_addr.sin_family = AF_INET; // host byte order
my_addr.sin_port = htons(MYPORT); // short, network byte order
my_addr.sin_addr.s_addr = INADDR_ANY; // auto-fill with my IP
memset(&(my_addr.sin_zero), '\0', 8); // zero the rest of the struct
 
// don't forget your error checking for these calls:
bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr));
 
listen(sockfd, BACKLOG);
 
sin_size = sizeof(struct sockaddr_in);
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);

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It's kind of a long shot... try to do

Code:

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sin_size = sizeof(their_addr);

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I know it's the same thing as sizeof(struct sockaddr_in), but you never know.

how did my previous post not solve the problem?

because he followed the guide word by word...
plus, I also call the function the same way, and it works just fine!

"works for me" is not very useful. A) Are you using C? If so then of course it works you might try upping your warning level. B) sockets are not very standard so god knows how they are implemented on your machine vs his. It sounds like he is using C++ in which cause his types need to match up, which was covered in my first response.

i was trying to rewrite it in C++, but was unsuccessful when compiling it with g++.
i guess my question was not fully asked. I was more interested in the reasoning why it works in C, and not in C++. I know now, but from your prior post, I did not understand that you were saying that unlike C, C++ requires types to match up. So my question for you now is... does the C++ standard and C standard differ in the implimentation of the function calls for sockets? I know from my reading that *nix and windows differ, but on *nix does it also differ between C and C++?

Because C is weakly typed and C++ is strongly typed. This means if 2 types don't match, for isntance a socklen_t* and a int*, then your C compiler will, at best, give you a warning. In C++ thiis is an error. And the BSD socket API is written in a sad attempt to provide some sort of inheritence style pointers (that is why things accept pointers to one type but you give it a pointer to another similar type) so in C++ you need to do a lot of explicit casting. You should be using static_cast for you casts by the way, C-style casts are frowned upon.
And no the API oes not differe. There is only one socket API on your system so it's the same for both languages.

Where did you guys get the socklen_t* from?
allow me to point you to the MSDN

Quote:

---

SOCKET accept(
SOCKET s,
struct sockaddr* addr,
int* addrlen
);

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Remember what I said about socket API's not being standard? Let me point you to the manpages on my machine:

Quote:

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int
accept(int s, struct sockaddr *addr, socklen_t *addrlen);

---

Any questions now Devil Panther?

I see your point and I bow before your knowledge :D
but never the less, we are talking about VC7 here, which implements the msdn.

Anyway, as orbitz said, just cast... ;) you never know :D

"implements the msdn"? MSDN is not a library or a verison of libc++, it's just a website with lots of information. it stands for microsoft developer network. VC7 has an implementaiton of Win32API and Winsock, which implements this behavior.

but if the msdn says it's int, then VC7 implemented it as int.

ok, forget about msdn...
Borland C++ 5.5 implemintation:

Code:

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SOCKET PASCAL FAR accept (
                          IN SOCKET s,
                          OUT struct sockaddr FAR *addr,
                          IN OUT int FAR *addrlen);

---

VC 6 implemintation:

Code:

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SOCKET PASCAL FAR accept (SOCKET s, struct sockaddr FAR *addr,
                          int FAR *addrlen);

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and even Bloodshed DevC++:

Code:

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SOCKET PASCAL accept(SOCKET,struct sockaddr*,int*);

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Because MSDN documents what Vc7 does, not the other way round. But this is certinaly pedantic and not worth continuing.

new question
i tried to consolidate my server and client in one program.
i created a program using both beej and madwizard.
i'm getting an error i have never seen.

Quote:

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Run-Time Check Failure #2 - Stack around the variable 'buffer2' was corrupted.

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here is the code that is involved with buffer2

Code:

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                        char buffer1[128]="Hello World", buffer2[128];
 
                        if (send(remoteSocket, buffer1, sizeof(buffer1), 0)==SOCKET_ERROR)
                        {
                                cout<<"Remote socket send Error"<<endl;
                                getch();
                                exit(1);
                        }
 
                        int bytesReceived = recv(localSocket, buffer2, sizeof(buffer2), 0);
 
                        buffer2[bytesReceived]='\0';
 
                        cout<<buffer2;
                        cout<<endl;
                        getch();

---

any help would be appreciated

never mind i fixed it with

Code:

---

        char buffer1[128]="Hello World", buffer2[128];
 
        if (send(remoteSocket, buffer1, sizeof(buffer1), 0)==SOCKET_ERROR)
        {
                  cout<<"Remote socket send Error"<<endl;
                  getch();
                  exit(1);
        }
 
        int bytesReceived = recv(localSocket, buffer2, sizeof(buffer2), 0);
 
        buffer2[bytesReceived-1]='\0';
 
        cout<<buffer2;
        cout<<endl;
        getch();

---

Two concerns about buffer2:

1) Are you allowed to initialize multiple char arrays on one line? I don't see why not, but it's possible.

2) If you receive 128 bytes, your code will run:

Code:

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buffer2[128] = '\0';

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Which is obviously unacceptable since it's only indexed up to 127.

i just figured that out.
check the post before yours.
thanks though.

Sorry - you beat me to it. :)

no worries, i have another question if you are willing to look at it.
if i want to convert this into an online chat program.
(1) is there a way to have the chat display sequentially on a command line interface?
i haven't mastered windows programming yet, i'm only good with console programs.
I want the full communication to resemble a sequential list of text like irc or other im programs.
i can only think of a way to post text then ask for input then post.
it would be anything like a sequential chat.

sizeof is not teh saem as strlen, Are you sure you want to send 128bytes even though you only use strlen("hello world") of them?

Quote:

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Originally Posted by xviddivxoggmp3

i haven't mastered windows programming yet, i'm only good with console programs.

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so... you are good at both :D

Quote:

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sizeof is not teh saem as strlen, Are you sure you want to send 128bytes even though you only use strlen("hello world") of them?

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good call, i will correct that now. are you willing to look at the rest of my code to tell me what other inefficient errors I made?

another question i have. how can i keep receiving and printing while not sending?

i tried strlen(buffer), and it didn't work. it stopped anything from being transmitted.

Code:

---

        char buffer1[128]="Hello World", buffer2[128];
 
        if (send(remoteSocket, buffer1, strlen(buffer1) , 0)==SOCKET_ERROR)
        {
                cout<<"Remote socket send Error"<<endl;
                getch();
                exit(1);
        }
 
        int bytesReceived = recv(localSocket, buffer2, strlen(buffer2) , 0);
 
        buffer2[bytesReceived-1]='\0';
 
        cout<<buffer2;
        cout<<endl;
        getch();

---

Quote:

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i tried strlen(buffer), and it didn't work. it stopped anything from being transmitted.

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You are going to have to be more specific. That sent strlen(buffer1) worth of bytes regardless of what your test may have shown.
Do you have a testcase to show what you mean?
http://ortdotlove.net/testcase.html to learn what a testcase is.
I have a feeling you are probably getting confused because you proably don't know C/C++ as well as you should and sockets are a bit more complex than you had in mind.

Quote:

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another question i have. how can i keep receiving and printing while not sending?

---

What do you mean here? Nobody says you have to send in order to recv? Are you trying to keep on calling recv and not getting any bytes? If this is the case then you have to realize that it takes time to send data over a socket and this time is several orders of magnitude slower than it takes for your code to reach the next recv call. So you try to recv with nothing there to you don't get any data. You need to learn about 'select' and 'poll'. They let you wait until there is something there to read so you don't waste calls on an socket with nothing around.

thanks for your vote of confidence.
i'm sorry the last post was only half complete due to i'm posting while at work.
tell me if this is not correct for the conversion.

Code:

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send(remoteSocket, buffer1, (strlen(buffer1)+1) , 0)==SOCKET_ERROR)

---

the reason why it was destroying my last data transfer was due to i was using strlen on my receive buffer, and it basically said receive an amount equivalent to an empty buffer. so nothing was received.
but you did have some constructive comments in regards to the strlen(), so thanks for that.
I think my next question that wasn't thoroughly asked earlier was, how would i have two processes running at the same time? i read a little on and found the terms mult-threaded.
i'm assuming this is how i could receive and send at the same time. does anyone have a really good multi-thread link for me to read, so i can determine if this is what i'm looking for?

What do you mean by 'two processes running at teh same time'. Do you mean your client and server run at the same time? If so just run each of them seperatly.
You dont' need threads for any of what you are doing and threads are quite complex and will only make things worse. Look up select as I already suggested, and please be more complete in what you mean by "two processes running at the same time".

You don't need to have 2 threads running for reading/sending. You can use non-blocking sockets for this. As orbitz explained above, threads are not necessary unless you need more processing done with other parts of your server. Honestly you shouldn't think of being multi-threaded until you can get the reading/writing w/o blocking.

If writing for windows, check out WSAAsyncSelect, or use Select() from
Beej's Guide . Orbitz is also right about defining what you mean, because from what I see, you want to run a server and client at the same time from the same app? Do you mean something else?

Another question on sockets.
Can you have a socket as a public object in a class?

Code:

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class SocketProgram
{
public:
    SocketProgram();
    ~SocketProgram();

    SOCKET localSocket;
    sockaddr_in localSockAddr;
};

---

Of course, why wouldn't you be able to?

and another question on sockets.

what is the scope of the sockaddr_in?
Once it has been declared, what scope does it have?

The same scope as any other variable. The scope rules do not apply special for sockaddr_in.