Send() not "sending" whole message

Martin_T · 11-18-2009, 06:45 PM

Code:

printf("\nPlease enter username : ");
					scanf( "%s", &username);
					printf("Please enter password : ");
					scanf( "%s", &password);
					send(sockfd, &username, strlen(&username), 0);
					break;

Can anyone see why this code is sending all but the first character?

MK27 · 11-18-2009, 06:49 PM

How is "username" declared? Your use of & in all three cases here is not appropriate if these are just normal char pointers.

quzah · 11-18-2009, 06:50 PM

You don't need the & for scanning into an array / pointer. Also, you probably want to print your input just to be sure it's what you think it is:

Code:

scanf( ... )
printf( "debug: \'%s\'\n", username );

Quzah.

cas · 11-18-2009, 06:50 PM

If your compiler is not complaining about strlen(&username), you've got your types wrong (or you forgot to #include <string.h>). If your compiler is complaining about strlen(&username), you should fix the problem; don't ignore warnings from a compiler, as they tend to be useful.

At the very least, you should remove all those ampersands. They cannot be right (except possibly the &username in send() is acceptable, but even then you can drop it). Without seeing all of your code, though, I can't definitively say what's going wrong. It'd be really helpful to see the declarations of username and password, at least.

Martin_T · 11-18-2009, 07:08 PM

Code:

     char *username;
    char *password;

Code:

     printf("\nPlease enter your new username : ");
					scanf( "%s", username);
					printf("Please enter  your password : ");
					scanf( "%s", password);
					send(sockfd, username, strlen(username), 0);
					break;

When run like this, as soon as i press enter after inputting the user name I get a segmentation fault.

quzah · 11-18-2009, 07:10 PM

You didn't actually allocate space for either pointer, did you?

Quzah.

Martin_T · 11-18-2009, 07:16 PM

Sorry, I am quite new to C and have not quite got to grips with the pointer stuff.

Originally I had

Code:

     char username;
    char password;

Code:

     printf("\nPlease enter your new username : ");
					scanf( "%s", &username);
					printf("Please enter  your password : ");
					scanf( "%s", &password);
					send(sockfd, &username, strlen(&username), 0);
					break;

But that read in all the text, however long just missing of the first character.

quzah · 11-18-2009, 07:21 PM

Code:

char justonecharacter;
char *pointertoacharacterbutnoactualallocatedmemory;
char arrayofXelementsofactualallocatedspace[ X ];

If you're using a pointer, then you need to make it point some place. That means you need something like malloc.

Quzah.

Martin_T · 11-18-2009, 07:32 PM

Thanks! I've now declared them, for example :

Code:

     char string[50];

is this bad practice?

MK27 · 11-18-2009, 07:37 PM

Quote:

Originally Posted by Martin_T

is this bad practice?

No, but then you will want to restrict the amount of input in the scanf line so you cannot overflow -- scanf("%49s") or something.

11-18-2009, 06:45 PM	#1
Martin_T Registered User Join Date: Nov 2009 Posts: 51	Send() not "sending" whole message Code: printf("\nPlease enter username : "); scanf( "%s", &username); printf("Please enter password : "); scanf( "%s", &password); send(sockfd, &username, strlen(&username), 0); break; Can anyone see why this code is sending all but the first character?
Martin_T is offline

11-18-2009, 06:49 PM	#2
MK27 critical genius Join Date: Jul 2008 Location: SE Queens Posts: 5,230	How is "username" declared? Your use of & in all three cases here is not appropriate if these are just normal char pointers. __________________ "A man can't just sit around." -- Larry Walters
MK27 is offline

11-18-2009, 06:50 PM	#3
quzah +++ OK NO CARRIER Join Date: Oct 2001 Posts: 10,643	You don't need the & for scanning into an array / pointer. Also, you probably want to print your input just to be sure it's what you think it is: Code: scanf( ... ) printf( "debug: \'%s\'\n", username ); Quzah. __________________ Hundreds of thousands of dipshits can't be wrong. Are you up for the suck?
quzah is offline

11-18-2009, 06:50 PM	#4
cas Registered User Join Date: Sep 2007 Posts: 452	If your compiler is not complaining about strlen(&username), you've got your types wrong (or you forgot to #include <string.h>). If your compiler is complaining about strlen(&username), you should fix the problem; don't ignore warnings from a compiler, as they tend to be useful. At the very least, you should remove all those ampersands. They cannot be right (except possibly the &username in send() is acceptable, but even then you can drop it). Without seeing all of your code, though, I can't definitively say what's going wrong. It'd be really helpful to see the declarations of username and password, at least.
cas is offline

11-18-2009, 07:10 PM	#6
quzah +++ OK NO CARRIER Join Date: Oct 2001 Posts: 10,643	You didn't actually allocate space for either pointer, did you? Quzah. __________________ Hundreds of thousands of dipshits can't be wrong. Are you up for the suck?
quzah is offline

11-18-2009, 07:16 PM	#7
Martin_T Registered User Join Date: Nov 2009 Posts: 51	Sorry, I am quite new to C and have not quite got to grips with the pointer stuff. Originally I had Code: char username; char password; Code: printf("\nPlease enter your new username : "); scanf( "%s", &username); printf("Please enter your password : "); scanf( "%s", &password); send(sockfd, &username, strlen(&username), 0); break; But that read in all the text, however long just missing of the first character.
Martin_T is offline

11-18-2009, 07:21 PM	#8
quzah +++ OK NO CARRIER Join Date: Oct 2001 Posts: 10,643	Code: char justonecharacter; char *pointertoacharacterbutnoactualallocatedmemory; char arrayofXelementsofactualallocatedspace[ X ]; If you're using a pointer, then you need to make it point some place. That means you need something like malloc. Quzah. __________________ Hundreds of thousands of dipshits can't be wrong. Are you up for the suck?
quzah is offline

11-18-2009, 07:32 PM	#9
Martin_T Registered User Join Date: Nov 2009 Posts: 51	Thanks! I've now declared them, for example : Code: char string[50]; is this bad practice?
Martin_T is offline

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