How to clear the buffer in C?

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I have a receiver buffer in which i am receiving data from the recv(); call i want to clear the buffer after receiving data from the recv(); call in to the buffer.

C++

#define DEFAULT_BUFLEN 512
char recvbuf[DEFAULT_BUFLEN];

int recvbuflen = DEFAULT_BUFLEN;
char common[276];
int main()
{

//After connect and send call...
iResult = recv(ThreadSocket, recvbuf, recvbuflen, 0);
            if ( iResult&gt;0 )
              {
for(int j=0;j<=iResult;j++)
common[j]=recvbuf[j];

//NOW I WANT TO CLEAR recvbuf.......
//fflush can't be used,how can i do so?

}

Please tell by pseudo code

Posted 16-Sep-12 22:32pm

Tarun Batra

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Graham Breach · Answer 1 · 2012-09-16T22:58:00

Solution 2

Why do you want to clear the buffer? Will it contain sensitive information?

I suggest you look up the memcpy() and memset() functions.

Also, your "recvbuf" is longer than "common", so copying from recvbuf to common could overflow, which is Very Bad.

Posted 16-Sep-12 22:58pm

Graham Breach

Comments

Tarun Batra 17-Sep-12 5:28am

Sir i want to copy the data of recvbuf into the common buffer,actually as i am making the socket connection,according to my documentation i should receive 138 bytes but i am receiving 276 bytes that is double of 138 bytes.
To avoid extra 138 bytes i am using the following code
iResult = recv(ThreadSocket, recvbuf, recvbuflen, 0);
if ( iResult > 0 )
{
int prev=0;
//prev= iResult;
if(prev!=iResult)
{

for(j=0;j<=iResult;j++);
common[j] = recvbuf[j];

}
prev= iResult;
}

Tarun Batra 17-Sep-12 11:21am

please reply this http://www.codeproject.com/Questions/460820/Can-u-give-me-an-idea-how-to-implement-this

CPallini · Answer 2 · 2012-09-16T23:09:00

Solution 3

You probably don't need to clear such buffer, anyway:

memset(recvbuf, 0, sizeof(recvbuf));

will do the job.

Tarun Batra wrote:

C++

for(int j=0;j<=iResult;j++)
common[j]=recvbuf[j];

As already noted by Graham Breach you are going to overrun the common buffer with such code.

Posted 16-Sep-12 23:09pm

CPallini

Comments

Tarun Batra 17-Sep-12 5:26am

Sir i want to copy the data of recvbuf into the common buffer,actually as i am making the socket connection,according to my documentation i should receive 138 bytes but i am receiving 276 bytes that is double of 138 bytes.

Tarun Batra 17-Sep-12 5:26am

my code is something like this:
iResult = recv(ThreadSocket, recvbuf, recvbuflen, 0);
if ( iResult > 0 )
{
int prev=0;
//prev= iResult;
if(prev!=iResult)
{

for(j=0;j<=iResult;j++);
common[j] = recvbuf[j];

}
prev= iResult;
}

CPallini 17-Sep-12 5:34am

If you need 138 bytes then why don't you ask for exactly 138 bytes?

Tarun Batra 17-Sep-12 5:40am

sir i send one request command to a machine and receive the response from the machine,the response should be 138 bytes but i am 276 bytes i get a response like this:-
Bytes received: 14
Bytes received: 14
Bytes received: 16
Bytes received: 16
Bytes received: 18
Bytes received: 18
Bytes received: 17
Bytes received: 17
Bytes received: 14
Bytes received: 14
Bytes received: 15
Bytes received: 15
Bytes received: 19
Bytes received: 19
Bytes received: 15
Bytes received: 15
Bytes received: 10
Bytes received: 10
this is the output of following statements:-
iResult = recv(ThreadSocket, recvbuf, recvbuflen, 0);
if ( iResult > 0 )
{ printf("Bytes received: %d\n", iResult);
}

CPallini 17-Sep-12 5:50am

I suppose you should post ALL the relevant code to get better help.

Tarun Batra 17-Sep-12 6:00am

#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "100"
int iResult;
SOCKET ConnectSocket = INVALID_SOCKET;
SOCKET ThreadSocket = INVALID_SOCKET;
static DWORD WINAPI FIComThreadEntry(LPVOID lpdwThreadParam);
HANDLE gui_ThreadHandle[4];
bool connect(char *host,int port, int timeout);
struct addrinfo *result = NULL,
*ptr = NULL,
hints;

char recvbuf[DEFAULT_BUFLEN];

int recvbuflen = DEFAULT_BUFLEN;
void ReadConfigSettings();
void GetIniFilePath();
void CreateLogFolder();
//time_t t;

int m_port;
char *port2;
char *ip1="192.168.15.168";
char *ip_serv;
char data[6]="CM00";
const char data1[]={0x43,0x4d,0x30,0x30,0x0f,0x0D};
const char data2[]={0x43,0x4d,0x30,0x30,0xf0,0x0D};//f0
SYSTEMTIME st,lt;

Log* wLog;
char *b;
int LOGLVL;
const char* szLogDir;
char IniFilePath[2500];
void datarecv();
#define Buflen 1400
char common[276];
//char Buf[MaxSize][Buflen];
int __cdecl main(int argc, char **argv)
{

/*time_t time;
time(&time);*/

WSADATA wsaData;
SOCKET ConnectSocket = INVALID_SOCKET;

u_long iMode = 0;
DWORD nTimeout = 5000; // 5 seconds
// Validate the parameters
if (argc != 2) {
printf("usage: %s server-name\n", argv[0]);
return 1;
}

// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != 0) {
printf("WSAStartup failed with error: %d\n", iResult);
return 1;
}

ZeroMemory( &hints, sizeof(hints) );
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;

// Resolve the server address and port
iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result);
if ( iResult != 0 ) {
printf("getaddrinfo failed with error: %d\n", iResult);
WSACleanup();
return 1;
}

// Attempt to connect to an address until one succeeds
for(ptr=result; ptr != NULL ;ptr=ptr->ai_next) {

// Create a SOCKET for connecting to server
ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype,
ptr->ai_protocol);
if (ConnectSocket == INVALID_SOCKET) {
printf("socket failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
/////////////////////////////////////////////////////////////////////////////
// Set the socket I/O mode: In this case FIONBIO
// enables or disables the blocking mode for the
// socket based on the numerical value of iMode.
// If iMode = 0, blocking is enabled;
// If iMode != 0, non-blocking mode is enabled.

iResult = ioctlsocket(ConnectSocket, FIONBIO, &iMode);
if (iResult != NO_ERROR)
printf("ioctlsocket failed with error: %ld\n", iResult);
/////////////////////////////////////////////////////////////////////////////

iResult = setsockopt(ConnectSocket, SOL_SOCKET, SO_RCVTIMEO, (const char*)&nTimeout, sizeof(DWORD));
if (iResult != NO_ERROR)
{
printf("\nSetsocopt fail with error :%d\n",WSAGetLastError());

return 0;
}

// Connect to server.
iResult = connect( ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
if (iResult == SOCKET_ERROR) {
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
break;
}

freeaddrinfo(result);

if (ConnectSocket == INVALID_SOCKET) {
printf("Unable to connect to server!\n");
WSACleanup();
return 1;
}

DWORD FIComThreadId;

gui_ThreadHandle[1] = CreateThread(NULL,0, (LPTHREAD_START_ROUTINE)FIComThreadEntry,(LPVOID)ConnectSocket, 0, &FIComThreadId);

if(gui_ThreadHandle[1] == NULL)
{
printf("Error while creating FIComThreadEntry thread.\n");
printf("Leaving from FIComThreadEntry\n");

return 0;
}
while(1);

}

static DWORD WINAPI FIComThreadEntry(LPVOID lpdwThreadParam)
{
ThreadSocket=(SOCKET)lpdwThreadParam;
data[4]=0x0F;
//data[4]=0xF0;
data[5]=0x0D;
int i=0;
int j;
//while(1)
{

iResult = send( ThreadSocket, data, (int)strlen(data), 0 );
if (iResult == SOCKET_ERROR)
{
printf("send failed with error: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}

printf("Bytes Sent: %ld\n", iResult);
int prev

Tarun Batra 17-Sep-12 6:04am

int w =0;
do {//WORKING

//iResult = recvfrom(ThreadSocket, recvbuf, recvbuflen, 0,ptr->ai_addr, (int *)ptr->ai_addrlen);
iResult = recv(ThreadSocket, recvbuf, recvbuflen, 0);
if ( iResult > 0 )
{

printf("Bytes received: %d\n", iResult);
}
else if ( iResult == 0 )
printf("Connection closed\n");
else
printf("recv failed with error: %d\n", WSAGetLastError()); } while( iResult > 0 ); return 0;
}

Tarun Batra 17-Sep-12 6:05am

its int prev=0; and then code followed by int w=0;

Andrewpeter · Answer 3 · 2012-09-16T22:45:00

Solution 1

You want to clear all contents of buffer? If that is right you can use a for loop to set elements of it to zero.

Posted 16-Sep-12 22:45pm

Andrewpeter

Comments

Tarun Batra 17-Sep-12 11:22am

please reply this http://www.codeproject.com/Questions/460820/Can-u-give-me-an-idea-how-to-implement-this