segmentation fault in fwrite function

ajaysahoo · #1 (**permalink**) 06-19-2009

Hi,
my code is written in proC and it is in UNIX(AIX).I have written a small code for writing data into a binary file,but while writing my program is giving core dump.

Here Is my code----

fpWriteFile = fopen(WriteFileName,"wb+");

CHAR *recvgen;

recvgen = (char *)malloc(sizeof(char)*NSE_MAX_PACKET_RECV_SIZE);

fwrite (recvgen,NSE_MAX_PACKET_RECV_SIZE,1,fpWriteFile );

GaneshCPUX · #2 (**permalink**) 06-19-2009

Please check whether fpWriteFile and fpWriteFileare valid pointers. Most of the time these are the pain points.

rakeshawasthi · #3 (**permalink**) 06-19-2009

You have not initialized recvgen. I mean, there is no value in that.
PS:- use code tags in your code please.

ajaysahoo · #4 (**permalink**) 06-19-2009

i am receiving data from socket ...Please find the codes for that...

memset(recvgen,' ',NSE_MAX_PACKET_RECV_SIZE);

recv_bytes = recvfrom(sockfd1,recvgen,NSE_MAX_PACKET_RECV_SIZE,0,(struct sockaddr *)&serv_addr,&clilen)

rakeshawasthi · #5 (**permalink**) 06-19-2009

Code:

memset(recvgen,'\0',NSE_MAX_PACKET_RECV_SIZE);

debug it and see what exactly are the values of each variable and exactly from which statement are you getting error. use printf for this.

ajaysahoo · #6 (**permalink**) 06-19-2009

i did the following code change...
memset(recvgen,'\0',NSE_MAX_PACKET_RECV_SIZE);

still same problem,i debug using dbx ...its showing segmentation fault at fwrite.

also sizeof(recvgen) is 4 where i have defined NSE_MAX_PACKET_RECV_SIZE=1050

redoubtable · #7 (**permalink**) 06-19-2009

I'm guessing the problem is either in WriteFileName or fwriting to a closed stream due to improper verification if fopen() fails.

The following code works under Linux

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define NSE_MAX_PACKET_RECV_SIZE 1050

int
main(int argc, char *argv[])
{

        FILE *fpWriteFile;
        char *recvgen;
        char WriteFileName[1024];

        if (argc != 2)
                exit(1);
        strncpy(WriteFileName, argv[1], 1024);
        if (strlen(argv[1]) >= 1024)
                WriteFileName[1023] = '\0';
        fpWriteFile = fopen(WriteFileName,"wb+");
        if (fpWriteFile == NULL)
                exit(1);
        recvgen = (char *)malloc(sizeof(char)*NSE_MAX_PACKET_RECV_SIZE);
        if (recvgen == NULL)
                exit(1);
        fwrite (recvgen,NSE_MAX_PACKET_RECV_SIZE,1,fpWriteFile);
        exit (0);
}

Code:

cc -o file file.c
./file `perl -e 'print "A" x 10'` && echo $? -> OK: 0
./file `perl -e 'print "A" x 1024'` ; echo $? -> NOT OK (failing with filename too long): 1

You won't have a segfault now, please try to just debug it with printf()s and find out the problem.

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