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TCP Client Server Program

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0

I am doing a programming assignment, and I have pretty much figured out the missing information from the skeleton code given, However, For the life of me I cannot figure out how to actually print the message recieved from the client!
int recv (int socket, char *buff, int buff_len,int flags)
I am using this filled in with the proper information, hopefully, to receive a message from the client. However I have no idea how to actually print it on the server!

I tried cout << buff; but that just seems to break the program.
I should also note I am doing this assignment in Putty.

c++

share|improve this question

asked Mar 25 at 4:58

user1313410user1313410

177

add a comment | 

0

I am doing a programming assignment, and I have pretty much figured out the missing information from the skeleton code given, However, For the life of me I cannot figure out how to actually print the message recieved from the client!
int recv (int socket, char *buff, int buff_len,int flags)
I am using this filled in with the proper information, hopefully, to receive a message from the client. However I have no idea how to actually print it on the server!

I tried cout << buff; but that just seems to break the program.
I should also note I am doing this assignment in Putty.

c++

share|improve this question

asked Mar 25 at 4:58

user1313410user1313410

177

add a comment | 

I am doing a programming assignment, and I have pretty much figured out the missing information from the skeleton code given, However, For the life of me I cannot figure out how to actually print the message recieved from the client!
int recv (int socket, char *buff, int buff_len,int flags)
I am using this filled in with the proper information, hopefully, to receive a message from the client. However I have no idea how to actually print it on the server!

I tried cout << buff; but that just seems to break the program.
I should also note I am doing this assignment in Putty.

c++

share|improve this question

asked Mar 25 at 4:58

user1313410user1313410

177

share|improve this question

asked Mar 25 at 4:58

user1313410user1313410

177

share|improve this question

asked Mar 25 at 4:58

user1313410user1313410

177

asked Mar 25 at 4:58

user1313410user1313410

177

asked Mar 25 at 4:58

user1313410user1313410

177

1 Answer
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oldest

votes

1

You didn't show the actual code you are using to receive and print the message, but the most likely reason that cout << buff; is misbehaving is because it expects its argument to point to a 0-terminated char-array, and recv() does not 0-terminate the data it writes into your array. Because of that, the printing logic in the << operator will iterate past the end of the array looking for a 0-terminator-byte, and invoke undefined behavior.

The simple way to avoid that problem is to add a 0-terminator byte yourself, like this:

 char buff[512];
 int numBytesReceived = recv(sockFD, buff, sizeof(buff)-1, 0);
 if (numBytesReceived > 0)
 
 buff[numBytesReceived] = ''; // place 0-terminator byte at end of received data
 cout << buff << endl; // now it's safe to print
 
 else if (numBytesReceived == 0) cout << "connection closed!" << endl;
 else perror("recv");

share|improve this answer

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Sorry I'm relatively new to C++, just took a basic class in it a long time ago. what exactly is a 0-terminated char-array? is it just an array with a as the last slot to tell cout to stop printing? Is there any other way to print it without all these extra steps? like printf,
  
  – user1313410
  Mar 25 at 5:21
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Would i be able to shorten this by simply adding '/0' to the end of buf before I send it over to the server?
  
  – user1313410
  Mar 25 at 5:25
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Also if i were to print out another array with cout, will it print out the entire array with no problems as long as i assign '' to the end
  
  – user1313410
  Mar 25 at 5:31
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A 0-terminated array is just any char array with a '' char to mark the end of the valid chars; that is how C-style strings indicate the end of the string. You could send the '' char across the network from the server if you want, but it wouldn't work reliably, since there is no guarantee that all the chars you send will be received together in the same recv() call. Any array with a at the end should get printed without problems.
  
  – Jeremy Friesner
  Mar 25 at 6:27
  
  

  
  
  
  

add a comment | 

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1

You didn't show the actual code you are using to receive and print the message, but the most likely reason that cout << buff; is misbehaving is because it expects its argument to point to a 0-terminated char-array, and recv() does not 0-terminate the data it writes into your array. Because of that, the printing logic in the << operator will iterate past the end of the array looking for a 0-terminator-byte, and invoke undefined behavior.

The simple way to avoid that problem is to add a 0-terminator byte yourself, like this:

 char buff[512];
 int numBytesReceived = recv(sockFD, buff, sizeof(buff)-1, 0);
 if (numBytesReceived > 0)
 
 buff[numBytesReceived] = ''; // place 0-terminator byte at end of received data
 cout << buff << endl; // now it's safe to print
 
 else if (numBytesReceived == 0) cout << "connection closed!" << endl;
 else perror("recv");

share|improve this answer

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Sorry I'm relatively new to C++, just took a basic class in it a long time ago. what exactly is a 0-terminated char-array? is it just an array with a as the last slot to tell cout to stop printing? Is there any other way to print it without all these extra steps? like printf,
  
  – user1313410
  Mar 25 at 5:21
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Would i be able to shorten this by simply adding '/0' to the end of buf before I send it over to the server?
  
  – user1313410
  Mar 25 at 5:25
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Also if i were to print out another array with cout, will it print out the entire array with no problems as long as i assign '' to the end
  
  – user1313410
  Mar 25 at 5:31
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A 0-terminated array is just any char array with a '' char to mark the end of the valid chars; that is how C-style strings indicate the end of the string. You could send the '' char across the network from the server if you want, but it wouldn't work reliably, since there is no guarantee that all the chars you send will be received together in the same recv() call. Any array with a at the end should get printed without problems.
  
  – Jeremy Friesner
  Mar 25 at 6:27
  
  

  
  
  
  

add a comment | 

1

You didn't show the actual code you are using to receive and print the message, but the most likely reason that cout << buff; is misbehaving is because it expects its argument to point to a 0-terminated char-array, and recv() does not 0-terminate the data it writes into your array. Because of that, the printing logic in the << operator will iterate past the end of the array looking for a 0-terminator-byte, and invoke undefined behavior.

The simple way to avoid that problem is to add a 0-terminator byte yourself, like this:

 char buff[512];
 int numBytesReceived = recv(sockFD, buff, sizeof(buff)-1, 0);
 if (numBytesReceived > 0)
 
 buff[numBytesReceived] = ''; // place 0-terminator byte at end of received data
 cout << buff << endl; // now it's safe to print
 
 else if (numBytesReceived == 0) cout << "connection closed!" << endl;
 else perror("recv");

share|improve this answer

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Sorry I'm relatively new to C++, just took a basic class in it a long time ago. what exactly is a 0-terminated char-array? is it just an array with a as the last slot to tell cout to stop printing? Is there any other way to print it without all these extra steps? like printf,
  
  – user1313410
  Mar 25 at 5:21
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Would i be able to shorten this by simply adding '/0' to the end of buf before I send it over to the server?
  
  – user1313410
  Mar 25 at 5:25
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Also if i were to print out another array with cout, will it print out the entire array with no problems as long as i assign '' to the end
  
  – user1313410
  Mar 25 at 5:31
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A 0-terminated array is just any char array with a '' char to mark the end of the valid chars; that is how C-style strings indicate the end of the string. You could send the '' char across the network from the server if you want, but it wouldn't work reliably, since there is no guarantee that all the chars you send will be received together in the same recv() call. Any array with a at the end should get printed without problems.
  
  – Jeremy Friesner
  Mar 25 at 6:27
  
  

  
  
  
  

add a comment | 

You didn't show the actual code you are using to receive and print the message, but the most likely reason that cout << buff; is misbehaving is because it expects its argument to point to a 0-terminated char-array, and recv() does not 0-terminate the data it writes into your array. Because of that, the printing logic in the << operator will iterate past the end of the array looking for a 0-terminator-byte, and invoke undefined behavior.

The simple way to avoid that problem is to add a 0-terminator byte yourself, like this:

 char buff[512];
 int numBytesReceived = recv(sockFD, buff, sizeof(buff)-1, 0);
 if (numBytesReceived > 0)
 
 buff[numBytesReceived] = ''; // place 0-terminator byte at end of received data
 cout << buff << endl; // now it's safe to print
 
 else if (numBytesReceived == 0) cout << "connection closed!" << endl;
 else perror("recv");

share|improve this answer

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167

 char buff[512];
 int numBytesReceived = recv(sockFD, buff, sizeof(buff)-1, 0);
 if (numBytesReceived > 0)
 
 buff[numBytesReceived] = ''; // place 0-terminator byte at end of received data
 cout << buff << endl; // now it's safe to print
 
 else if (numBytesReceived == 0) cout << "connection closed!" << endl;
 else perror("recv");

share|improve this answer

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167

answered Mar 25 at 5:06

Jeremy FriesnerJeremy Friesner

41.4k1182167