Segmenatation fault in fread - c

Question

I encounter segmenatation fault in fread while I am reading 1500 or more ethernet data packets. Here "test2" is the binary file whose file size is 22.6MB. 1132 is the number of useful data points in each packet and 142 points carries header information hence it is skipped.
here is the main program:
void main()
{
int count;
FILE *fp;
long file_size;
unsigned char rawdata[1132];
fp=fopen("test2","rb");
if(fp==-1)
{
printf("unsucessful");
exit(0);
}
long int before=ftell(fp);
fseek(fp,0,SEEK_END);
file_size=ftell(fp);
rewind(fp);
long int after=ftell(fp);
//skip first 142 bytes(header information)since its not required
fseek(fp,142,SEEK_SET);
long int s=ftell(fp);
int length_of_fft=4096;
int buffer_width=128;
int buffer_depth=1024;
int k,aa,payloadindex=0,l=0,j,a;
int no_of_data_pts_to_be_read=1132;
int no_of_ethernet_pkts_to_be_read=1500;
int q=no_of_ethernet_pkts_to_be_read*buffer_depth;
unsigned char payload[q];
unsigned int payloadint[q];
int no_of_data_pks_read=0;
int reading_for_first_time=1;
unsigned char data_from_file[no_of_ethernet_pkts_to_be_read][buffer_depth];
int addr_offset_in_inarray=0;
int udp_counter_values[no_of_ethernet_pkts_to_be_read];
unsigned int rawdataint[1132];
long int size;
count=0;
for(a=0; a<no_of_ethernet_pkts_to_be_read; a++)
{
int p=fread(rawdata,1 ,sizeof(rawdata), fp);
count=p;
//----------- to check if all data points have been read, i,e the pointer must be at a position wich is a multiple of 1132 which is[(1274-142=1132)*(a+1)],( since 142 bytes were skipped in the beginning )
printf("\n\n %d\t Start=%x\t\t Stop=%x\t Count=%d\t Address=%x",no_of_data_pks_read, rawdata[0], rawdata[sizeof(rawdata)-1],count,
ftello(fp));
if(count==no_of_data_pts_to_be_read)
{
printf("\nNumber of data points read in packet %d (of %d) is %d ",no_of_data_pks_read, no_of_ethernet_pkts_to_be_read, count);
reading_for_first_time=0;
//--------------converting char array rawdata into int array and then call udp
for(i=0;i<1132;i++)
rawdataint[i]=rawdata[i]-'\0';
udp_counter_values[a]=check_UDPpacketCount(&addr_offset_in_inarray, &rawdataint,10,no_of_data_pks_read,1132);
// printf("\n--------udp:: %d ",udp_counter_values[a]);
//-----------------create new mat and compute payload and put the contents of array rawwdata into the respective row of the new matrix
int k,t,w,time=0;
for(k=0,l=addr_offset_in_inarray;l<sizeof(rawdata),k<1024;k++,l++)
{
data_from_file[no_of_data_pks_read][k]=rawdata[l];
// printf("\n datafile:%d",data_from_file[no_of_data_pks_read][k]);
}
for(t=0;t<1024;t++)
{
payload[payloadindex++]=data_from_file[no_of_data_pks_read][t];
}
no_of_data_pks_read++;
}
else
{
count=0;
printf("\n not equal, exiting ");
exit(0);
}
}
//------convert payload to int array and send to data extraction function
for(i=0;i<sizeof(payload);i++)
{
payloadint[i]=payload[i]-'\0';
}
printf(" sizepayload: %d", sizeof(payload));
size=sizeof(payload);
data_extraction(size, payloadint,buffer_depth,buffer_width,length_of_fft);
printf("\n s:%d",file_size);
printf("\n ft:%x",ftell(fp));
printf("\n****----end----****");
fclose(fp);
}

Answer 1

As it has already been mentioned that you might be using up all your stack, try making all statically allocated variables global or use dynamic allocation. That should improve your situation.

Answer 2

fopen() returns a NULL pointer upon error, not -1.
If fopen has failed, you go on and do file operations with a NULL pointer.
This is wrong:
fp=fopen("test2","rb");
if(fp==-1)
{
printf("unsucessful");
exit(0);
}
It should be (and watch my use of whitespace)
fp = fopen("test2", "rb");
if (fp == NULL) {
printf("Could not open test2\n"); /* A meaningful error message */
exit(0);
}

Answer 3

There are few errors in your code.
1.you need check fp==NULL instead of fp==-1 when ever fopen() fails it returns NULL
2.in for loop you are using comma ,I guessing that is AND.
for(k=0,l=addr_offset_in_inarray;l<sizeof(rawdata),k<1024;k++,l++)
^
for(k=0,l=addr_offset_in_inarray;((l<sizeof(rawdata) )&& (k<1024));k++,l++)
^^
3.did not declared variable i.
warnings need to remove
You did not used many variables even though they are initialized with values
type mismatch while printing.
MODIFIED CODE
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void main()
{
int count,i;
FILE *fp;
long file_size;
unsigned char rawdata[1132];
fp=fopen("test2","rb");
if(fp==NULL)
{
printf("unsucessful");
exit(0);
}
long int before=ftell(fp);
fseek(fp,0,SEEK_END);
file_size=ftell(fp);
rewind(fp);
long int after=ftell(fp);
//skip first 142 bytes(header information)since its not required
fseek(fp,142,SEEK_SET);
long int s=ftell(fp);
int length_of_fft=4096;
int buffer_width=128;
int buffer_depth=1024;
int k,aa,payloadindex=0,l=0,j,a;
int no_of_data_pts_to_be_read=1132;
int no_of_ethernet_pkts_to_be_read=1500;
int q=no_of_ethernet_pkts_to_be_read*buffer_depth;
unsigned char payload[q];
unsigned int payloadint[q];
int no_of_data_pks_read=0;
int reading_for_first_time=1;
unsigned char data_from_file[no_of_ethernet_pkts_to_be_read][buffer_depth];
int addr_offset_in_inarray=0;
int udp_counter_values[no_of_ethernet_pkts_to_be_read];
unsigned int rawdataint[1132];
long int size;
count=0;
for(a=0; a<no_of_ethernet_pkts_to_be_read; a++)
{
int p=fread(rawdata,1 ,sizeof(rawdata), fp);
count=p;
//----------- to check if all data points have been read, i,e the pointer must be at a position wich is a multiple of 1132 which is[(1274-142=1132)*(a+1)],( since 142 bytes were skipped in the beginning )
printf("\n\n %d\t Start=%x\t\t Stop=%x\t Count=%d\t Address=%x",no_of_data_pks_read, rawdata[0], rawdata[sizeof(rawdata)-1],count,(unsigned int) ftell(fp));
if(count==no_of_data_pts_to_be_read)
{
printf("\nNumber of data points read in packet %d (of %d) is %d ",no_of_data_pks_read, no_of_ethernet_pkts_to_be_read, count);
reading_for_first_time=0;
//--------------converting char array rawdata into int array and then call udp
for(i=0;i<1132;i++)
rawdataint[i]=rawdata[i]-'\0';
udp_counter_values[a]=check_UDPpacketCount(&addr_offset_in_inarray, &rawdataint,10,no_of_data_pks_read,1132);
// printf("\n--------udp:: %d ",udp_counter_values[a]);
//-----------------create new mat and compute payload and put the contents of array rawwdata into the respective row of the new matrix
int k,t,w,time=0;
for(k=0,l=addr_offset_in_inarray;(l<sizeof(rawdata)|| k<1024);k++,l++)
{
data_from_file[no_of_data_pks_read][k]=rawdata[l];
// printf("\n datafile:%d",data_from_file[no_of_data_pks_read][k]);
}
for(t=0;t<1024;t++)
{
payload[payloadindex++]=data_from_file[no_of_data_pks_read][t];
}
no_of_data_pks_read++;
}
else
{
count=0;
printf("\n not equal, exiting ");
exit(0);
}
}
//------convert payload to int array and send to data extraction function
for(i=0;i<sizeof(payload);i++)
{
payloadint[i]=payload[i]-'\0';
}
printf(" sizepayload: %ld", sizeof(payload));
size=sizeof(payload);
data_extraction(size, payloadint,buffer_depth,buffer_width,length_of_fft);
printf("\n s:%ld",file_size);
printf("\n ft:%x",(unsigned int)ftell(fp));
printf("\n****----end----****");
fclose(fp);
}

Answer 4

If you're on a Unix-like platform, you could replace the fopen, fread, fseek calls with the raw system-calls just to see what happens.
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
int fd = open("test2", O_RDONLY);
if (fd < 0) {
printf("Could not open test2\n");
exit(0);
}
And then use read() instead of fread(), lseek() instead of fseek() ,etc.