segmentation error during structured array (part of ip lookup)

I have been facing with this problem for almost 5 days.
This is part that grab IP address from file and store it as array.
so hash tables are supposed to be like this:

hashtable[length].which_element_of_table.IP_add

Code:

---

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
//*************
struct ttyp
{
    unsigned int index;
    struct prtyp{
        unsigned char len;
        unsigned char port;
        unsigned int ip;
        } *prefix;
};

int num_entry=0;
struct ttyp *htable;

// READ IP FROM TEXT FILE
void read_table(char *str,unsigned int *ip,int *len,unsigned int *nexthop)
{
    char tok[]="./";
    char buf[100],*str1;
    unsigned int n[4];
    sprintf(buf,"%s\0",strtok(str,tok));
    n[0]=atoi(buf);
    sprintf(buf,"%s\0",strtok(NULL,tok));
    n[1]=atoi(buf);
    sprintf(buf,"%s\0",strtok(NULL,tok));
    n[2]=atoi(buf);
    sprintf(buf,"%s\0",strtok(NULL,tok));
    n[3]=atoi(buf);
    *nexthop=n[2];
    str1=(char *)strtok(NULL,tok);
    if(str1!=NULL)
    {
        sprintf(buf,"%s\0",str1);
        *len=atoi(buf);
    }
    else
    {
        if(n[1]==0&&n[2]==0&&n[3]==0)
            *len=8;
        else if(n[2]==0&&n[3]==0)
            *len=16;
        else if(n[3]==0)
            *len=24;
    }
    *ip=n[0];
    *ip<<=8;
    *ip+=n[1];
    *ip<<=8;
    *ip+=n[2];
    *ip<<=8;
    *ip+=n[3];
}

//BUILD HASH TABLE
void hash_table(char *file_name)
{
    int count,z;
    FILE *fp;
    int len;
    char string[100];
    unsigned int ip,nexthop;
    fp=fopen(file_name,"r");

    while(fgets(string,50,fp)!=NULL)
    {
        read_table(string,&ip,&len,&nexthop);
        num_entry++;
    }
    rewind(fp);
    //prefix=(struct prtyp *)malloc(num_entry*sizeof(struct prtyp));  // i think this line is unnecessary, so i comment it
    htable=(struct ttyp *)malloc(32*num_entry*sizeof(struct ttyp));
    for(count=1; count<=32; count++){
        htable[count].index=0;  //counter initialization
        }
    while(fgets(string,50,fp)!=NULL){
        read_table(string,&ip,&len,&nexthop);

        z=htable[len].index;
        htable[len].prefix[z].ip=ip;
        htable[len].prefix[z].port=nexthop;
        htable[len].index++;
        }
}

//MAIN

int main(int argc,char *argv[])
{
    hash_table(argv[1]);
    printf("\n=================================");
    printf("\nTotal prefix in txt file: %d", num_entry);
    printf("\n=================================\n");
    for(y=1;y<=32;y++){
        if(htable[y].index)
        printf("Table[%d] value numbers: %d\n",y,htable[y].index);
        }
return0;
}

---

I thought i allocate enough memory htable pointer.

But still get:
Segmentation fault

Anyone help ? :)


Thanks,
Kane

It depends on where you get the segmentation fault. Can you post the stack trace, please?

You are only allocating memory for your ttyp, never for the prefix inside. You are then attempting to write at the garbage memory it points to.

Also all your for loops are wrong. Valid array indexes are 0 .. number of elements - 1 in C.
Kurt

root@kane-BM5220-BM5320-BM5620:/home/kane/my_files/course_files/midterm_project# gcc 8_May.c -o test2
root@kane-BM5220-BM5320-BM5620:/home/kane/my_files/course_files/midterm_project# ./test1 traffic.txt table.txt
Segmentation fault

Quote:

---

Originally Posted by eegii_evol

root@kane-BM5220-BM5320-BM5620:/home/kane/my_files/course_files/midterm_project# gcc 8_May.c -o test2
root@kane-BM5220-BM5320-BM5620:/home/kane/my_files/course_files/midterm_project# ./test1 traffic.txt table.txt
Segmentation fault

---

reply

Zuk: I knew array starts from 0. But i tried to represent array number as length directly. that was my mistake thanks Kurt. Let me try now.

Claudiu: In this case how should I declare structures.
Actually I did this individually, but still got error. Like this:

Code:

---

struct ttyp
{
    unsigned int index;
    struct prtyp *prefix;
};

struct prtyp{
    unsigned char len;
    unsigned char port;
    unsigned int ip;
};
struct prtyp *prefix;
struct ttyp *htable;
prefix=(struct prtyp *)malloc(num_entry*sizeof(struct prtyp));
htable=(struct ttyp *)malloc(32*sizeof(struct ttyp));

---

1) That's not a stack trace.
2) You need to get yourself a proper debugger, not just run the program.
3) You need to compile with warnings on:

gcc -O3 -g3 -Wall -c -fmessage-length=0 -otest.o ..\test.c
..\test.c: In function 'read_table':
..\test.c:24: warning: embedded '\0' in format
..\test.c:26: warning: embedded '\0' in format
..\test.c:28: warning: embedded '\0' in format
..\test.c:30: warning: embedded '\0' in format
..\test.c:36: warning: embedded '\0' in format
..\test.c: In function 'main':
..\test.c:96: error: 'y' undeclared (first use in this function)
..\test.c:96: error: (Each undeclared identifier is reported only once
..\test.c:96: error: for each function it appears in.)
..\test.c:100: error: 'return0' undeclared (first use in this function)
Build error occurred, build is stopped
Time consumed: 4535 ms.

The last one might just be because your formatting appears screwed on the code drop you did. But before I even TRY to run the program, I've got those errors. And my debugger breakpoints right at the point where something goes wrong with one click.

Try actually WORKING OUT WHAT'S WRONG. Even assuming that you don't have a proper debugger, stick a printf that you can spot into the functions so you at least know if it crashes before a certain line or after it. It would take two minutes to do that on EVERY line of code, run it, and work out what line it crashes on yourself. From there, it's a short step to work out WHY that line crashed and what caused that to happen (e.g. overflow, etc.) and how to fix it.

But just running a program with ZERO WARNINGS ENABLED and then expecting it to magically tell you what's wrong is like trying to diagnose a car engine fault by getting on the motorway and telling the recovery vehicle "It just stopped" (not how, when, what you did, were, what the gauges read at the time, what noises it made, etc.)

Guess that is what you want

Code:

---

struct ttyp
{
    unsigned int index;
    struct prtyp *prefix;
};
 
struct prtyp{
    unsigned char len;
    unsigned char port;
    unsigned int ip;
};

struct ttyp *htable;

htable=malloc(32*sizeof(struct ttyp));
htable->prefix=malloc(num_entry*sizeof(struct prtyp));

---

Kurt

I have changed code some parts by fixing arrays and separating structures.

Code:

---

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
struct ttyp
{
    unsigned int index;
    struct prtyp *prefix;
};

struct prtyp{
    unsigned char len;
    unsigned char port;
    unsigned int ip;
} ;

struct prtyp *prefix;
struct ttyp *htable;
int num_entry=0;

////////////////////////////////////////////////////////////////////////////////////
void read_table(char *str,unsigned int *ip,int *len,unsigned int *nexthop)
{
    char tok[]="./";
    char buf[100],*str1;
    unsigned int n[4];
    sprintf(buf,"%s\0",strtok(str,tok));
    n[0]=atoi(buf);
    sprintf(buf,"%s\0",strtok(NULL,tok));
    n[1]=atoi(buf);
    sprintf(buf,"%s\0",strtok(NULL,tok));
    n[2]=atoi(buf);
    sprintf(buf,"%s\0",strtok(NULL,tok));
    n[3]=atoi(buf);
    *nexthop=n[2];
    str1=(char *)strtok(NULL,tok);
    if(str1!=NULL)
    {
        sprintf(buf,"%s\0",str1);
        *len=atoi(buf);
    }
    else
    {
        if(n[1]==0&&n[2]==0&&n[3]==0)
            *len=8;
        else if(n[2]==0&&n[3]==0)
            *len=16;
        else if(n[3]==0)
            *len=24;
    }
    *ip=n[0];
    *ip<<=8;
    *ip+=n[1];
    *ip<<=8;
    *ip+=n[2];
    *ip<<=8;
    *ip+=n[3];
}

//********************************************************
void hash_table(char *file_name)
{
    int count,z;
    FILE *fp;
    int len;
    char string[100];
    unsigned int ip,nexthop;
    fp=fopen(file_name,"r");

    while(fgets(string,50,fp)!=NULL)
    {
        read_table(string,&ip,&len,&nexthop);
        num_entry++;
    }
    rewind(fp);
    prefix=(struct prtyp *)malloc(num_entry*sizeof(struct prtyp));
    htable=(struct ttyp *)malloc(32*sizeof(struct ttyp));
    for(count=0; count<=31; count++){
        htable[count].index=0;  //counter initialization
        }
    while(fgets(string,50,fp)!=NULL){
        read_table(string,&ip,&len,&nexthop);

        z=htable[len-1].index;
        htable[len-1].prefix[z].ip=ip;
        htable[len-1].index++;
        }
}

//*********************************************************
int main(int argc,char *argv[])
{
    if(argc!=3)
    {
        printf("Please execute the file as the following way:\n");
        printf("%s  routing_table_file_name  query_table_file_name\n",argv[0]);
        exit(1);
    }
    //set_query(argv[2]);
    int y;


    hash_table(argv[1]);
    printf("\n=================================");
    printf("\nTotal prefix in txt file: %d", num_entry);
    printf("\n=================================\n");
    for(y=0;y<=31;y++){
        if(htable[y].index)
        printf("Table[%d] value numbers: %d\n",y+1,htable[y].index);
        }
    printf("TEST: %d",htable[23].prefix[0].ip); //there is 23 length exists in file

    return 0;

}

---

TRACE:

root@kane-BM5220-BM5320-BM5620:/home/kane/my_files/course_files/midterm_project# gcc -O3 -g3 -Wall -c -fmessage-length=0 -otest.o trash.c
trash.c: In function ‘read_table’:
trash.c:26:5: warning: embedded ‘\0’ in format [-Wformat-contains-nul]
trash.c:28:5: warning: embedded ‘\0’ in format [-Wformat-contains-nul]
trash.c:30:5: warning: embedded ‘\0’ in format [-Wformat-contains-nul]
trash.c:32:5: warning: embedded ‘\0’ in format [-Wformat-contains-nul]
trash.c:38:9: warning: embedded ‘\0’ in format [-Wformat-contains-nul]



Thanks,
Kane

Zuk,

Ohh thanks man, I gotta try it now.

Quote:

---

Originally Posted by ledow

1) That's not a stack trace.
2) You need to get yourself a proper debugger, not just run the program.
3) You need to compile with warnings on:

gcc -O3 -g3 -Wall -c -fmessage-length=0 -otest.o ..\test.c
..\test.c: In function 'read_table':
..\test.c:24: warning: embedded '\0' in format
..\test.c:26: warning: embedded '\0' in format
..\test.c:28: warning: embedded '\0' in format
..\test.c:30: warning: embedded '\0' in format
..\test.c:36: warning: embedded '\0' in format
..\test.c: In function 'main':
..\test.c:96: error: 'y' undeclared (first use in this function)
..\test.c:96: error: (Each undeclared identifier is reported only once
..\test.c:96: error: for each function it appears in.)
..\test.c:100: error: 'return0' undeclared (first use in this function)
Build error occurred, build is stopped
Time consumed: 4535 ms.

The last one might just be because your formatting appears screwed on the code drop you did. But before I even TRY to run the program, I've got those errors. And my debugger breakpoints right at the point where something goes wrong with one click.

Try actually WORKING OUT WHAT'S WRONG. Even assuming that you don't have a proper debugger, stick a printf that you can spot into the functions so you at least know if it crashes before a certain line or after it. It would take two minutes to do that on EVERY line of code, run it, and work out what line it crashes on yourself. From there, it's a short step to work out WHY that line crashed and what caused that to happen (e.g. overflow, etc.) and how to fix it.

But just running a program with ZERO WARNINGS ENABLED and then expecting it to magically tell you what's wrong is like trying to diagnose a car engine fault by getting on the motorway and telling the recovery vehicle "It just stopped" (not how, when, what you did, were, what the gauges read at the time, what noises it made, etc.)

---

I really appreciate for your suggestion and help. Thank you for your time. I will do my best on it.