Segmentation Fault and Debugging with Valgrind

Question

I am having a Segmentation problem probably in this segment of the code, Used Valgrind but i am new at this and cannot understand what it means.Can someone help me remove the errror from the following code. Response of Valgrind is also there. After the code the response of valgrind is given.

send_file1=fopen("Document.txt","rb");
cout<<"what";
if(send_file1==NULL) 
{
if(int nofile = sendto(conn_sock , NoFile , sizeof(NoFile) , 0 ,(struct sockaddr *)&client_addr , sizeof(client_addr))==-1) //Sendin ACK
{
    cout<<"ERROR"<<endl;
    exit(1);
}

}
if(int accept = sendto(conn_sock , accepted , sizeof(accepted) , 0 ,(struct sockaddr *)&client_addr , sizeof(client_addr))==-1) //Sendin ACK
{
    cout<<"ERROR"<<endl;
    exit(1);
}
cout<<"CHECK"<<endl;
fseek (send_file1 , 0 , SEEK_END);
length = ftell (send_file1);
rewind (send_file1);

// allocate memory to contain the whole file:
Buffer = (char*) malloc (sizeof(char)*length);
if (Buffer == NULL) {fputs ("Memory error",stderr); exit (2);}

// copy the file into the buffer:
Read_byt = fread (Buffer,1,length,send_file1);
if (Read_byt != length) {fputs ("Reading error",stderr); exit (3);}



==11113== Invalid read of size 2
==11113==    at 0x41C924D: fseek (fseek.c:40) 
==11113==    by 0x8049B34: main (in /home/mishal/Downloads/Work Moby/Computer     Networks/Project/Phase 1/execute)
==11113==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==11113==  
==11113== 
==11113== Process terminating with default action of signal 11 (SIGSEGV)
==11113==  Access not within mapped region at address 0x0
==11113==    at 0x41C924D: fseek (fseek.c:40)
==11113==    by 0x8049B34: main (in /home/mishal/Downloads/Work Moby/Computer Networks/Project/Phase 1/execute)
==11113==  If you believe this happened as a result of a stack
==11113==  overflow in your program's main thread (unlikely but
==11113==  possible), you can try to increase the size of the
==11113==  main thread stack using the --main-stacksize= flag.
==11113==  The main thread stack size used in this run was 8388608.
==11113== 
==11113== HEAP SUMMARY:
==11113==     in use at exit: 9,067 bytes in 8 blocks
==11113==   total heap usage: 9 allocs, 1 frees, 9,419 bytes allocated
==11113== 
==11113== LEAK SUMMARY:
==11113==    definitely lost: 500 bytes in 5 blocks
==11113==    indirectly lost: 0 bytes in 0 blocks
==11113==      possibly lost: 0 bytes in 0 blocks
==11113==    still reachable: 8,567 bytes in 3 blocks
==11113==         suppressed: 0 bytes in 0 blocks
==11113== Rerun with --leak-check=full to see details of leaked memory
==11113== 
==11113== For counts of detected and suppressed errors, rerun with: -v
==11113== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 19 from 8)

Answer 1

Compile your code with the -g (debug flag) to get more information, such as the location of the error in your source code, from valgrind. It looks like the file you are opening does not exist, so make sure you are checking the return values of external calls (ie, fopen , fseek , ...).