Thread: student database with linked list access violation (segmentation fault) problem

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Code:

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#include<string.h>
#include<dos.h>


struct stud
{
    int rn,id,ph;
    char add[30],na[20],d[15],in[5];
    struct stud *next;
}*h= NULL ,*p,*q,*t;


void add()
{
    p = new stud;
    printf("\nEnter the Initials of Student : ");
    scanf("%s",&p->in);
    printf("\nEnter the Last Name of Student : ");
    scanf("%s",&p->na);
    printf("\nEnter the ID of Student : ");
    scanf("%d",&p->id);
    printf("\nEnter the Roll No. of Student : ");
    scanf("%d",&p->rn);
    printf("\nEnter the Ph No. of Student : ");
    scanf("%d",&p->ph);
    printf("\nEnter the Address of Student : ");
    scanf("%s",&p->add);
    printf("\nEnter the D.O.B. of Student(dd/mm/yyyy) : ");
    scanf("%s",&p->d);


    p->next=NULL;


    if(h==NULL)
    {
        h=p;
    }
    else
    {
        q=h;
        while(q->next!=NULL)
            q=q->next;
        q->next=p;
    }
}


void addAt(int r)
{
    q=h;
    while(q->rn!=r || q==NULL)
        q=q->next;
    if(q->rn==r)
    {
        p =(stud *)malloc(sizeof(stud));
        printf("\nEnter the Initials of Student : ");
        scanf("%s",&p->in);
        printf("\nEnter the Last Name of Student : ");
        scanf("%s",&p->na);
        printf("\nEnter the ID of Student : ");
        scanf("%d",&p->id);
        printf("\nEnter the Roll No. of Student : ");
        scanf("%d",&p->rn);
        printf("\nEnter the Ph No. of Student : ");
        scanf("%d",&p->ph);
        printf("\nEnter the Address of Student : ");
        scanf("%s",&p->add);
        printf("\nEnter the D.O.B. of Student(dd/mm/yyyy) : ");
        scanf("%s",&p->d);
        p->next=q->next;
        q->next=p;


    }
    else
    {
        printf("\n\nRecord Not Found.");
    }
}




void delAt(int r)
{
    q=h;
    while((q->next)->rn!=r || q==NULL)
        q=q->next;
    if((q->next)->rn==r)
    {
        q->next=(q->next)->next;
        printf("\n\nRecord Deleted.");


    }
    else
        printf("\n\nRecord Not Found.");
}


void modAt(int id)
{
    q=h;
    int ch;
    while(q->id!=id && q!=NULL)
        q=q->next;
    if(q->id==id)
    {


        printf("******* MODIFY *******\n1.Name Initials\n2.Last Name");
        printf("\n3.Roll No.\n4.Phone\n5.Add\n6.D.O.B.:\nEnter choice: ");
        scanf("%d",&ch);
        switch(ch)
        {
            case 1 :  printf("\n\nEnter the Initials of Student : ");
                      scanf("%s",&q->in);break;
            case 2 :  printf("\nEnter the Last Name of Student : ");
                      scanf("%s",&q->na);break;
            case 3 :  printf("\nEnter the Roll No. of Student : ");
                      scanf("%d",&q->rn);break;
            case 4 :  printf("\nEnter the Ph No. of Student : ");
                      scanf("%d",&q->ph);break;
            case 5 :  printf("\nEnter the Address of Student : ");
                      scanf("%s",&q->add);break;
            case 6 :  printf("\nEnter the D.O.B. of Student(dd/mm/yyyy) : ");
                      scanf("%s",&q->d);break;
        }
    }
    else
        printf("\nRecord not Found.");
}


void search(char ni[5])
{
    int flag=0;
    q=h;


    while(q!=NULL)
    {
        if(stricmp(q->in,ni)==0)
        {
            flag=1;
            printf("\n\nInitals of Student :   %s ",q->in);
            printf("\n\nLast Name of Student : %s ",q->na);
            printf("\n\nID of Student :        %d ",q->id);
            printf("\n\nRoll No. of Student :  %d",q->rn);
            printf("\n\nPh No. of Student :    %d",q->ph);
            printf("\n\nAddress of Student :   %s",q->add);
            printf("\n\nD.O.B. of Student :    %s",q->d);
            printf("\n\n\n");
        }
        q=q->next;
    }
    if(flag==0)
        printf("\n\nNo Match Found.");
}


void sort()
{
    p=h;
    while(p!=NULL)
    {
        q=h;
        while(q!=NULL)
        {
            if(stricmp(q->in,(q->next)->in)>0)
            {
                strcpy(t->in,q->in);
                strcpy(t->na,q->na);
                t->id=q->id;
                t->rn=q->rn;
                t->ph=q->ph;
                strcpy(t->add,q->add);
                strcpy(t->d,q->d);




                strcpy(q->in,(q->next)->in);
                strcpy(q->na,(q->next)->na);
                q->id=  (q->next)->id;
                q->rn=  (q->next)->rn;
                q->ph=  (q->next)->ph;
                strcpy(q->add,(q->next)->add);
                strcpy(q->d,(q->next)->d);


                strcpy((q->next)->in,t->in);
                strcpy((q->next)->na,t->na);
                (q->next)->id = t->id;
                (q->next)->rn = t->rn;
                (q->next)->ph = t->ph;
                strcpy((q->next)->add,t->add);
                strcpy((q->next)->d,t->d);


            }
            q=q->next;
        }
        p=p->next;
    }
}
void disp()
{
    p=h;


    while(p!=NULL)
    {
        printf("\nInitals of Student :   %s ",p->in);
        printf("\nName of Student :      %s ",p->na);
        printf("\nID of Student :        %d ",p->id);
        printf("\nRoll No. of Student :  %d",p->rn);
        printf("\nPh No. of Student :    %d",p->ph);
        printf("\nAddress of Student :   %s",p->add);
        printf("\nD.O.B. of Student :    %s",p->d);
        printf("\n\n");
        p=p->next;
    }
}


main()
{
    int ch=0,r;
    char ni[5];


    while(ch!=8)
    {


        printf("1.Add the Record.\n\n2.Add Record at Locn.\n\n3.Delete Record.");
        printf("\n\n4.Modify Record.\n\n5.Search Record.\n\n6.Sort Records.");
        printf("\n\n7.Display\n\n8.Exit");
        printf("\n\nEnter the Choice: ");
        scanf("%d",&ch);
        switch(ch)
        {
            case 1:
                add();
                break;


            case 2:
                printf("\nEnter the Roll No. : ");
                scanf("%d",&r);
                addAt(r);
                break;


            case 3:
                printf("\nEnter the Roll No. : ");
                scanf("%d",&r);
                delAt(r);
                break;


            case 4:
                printf("\nEnter the ID : ");
                scanf("%d",&r);
                modAt(r);
                break;


            case 5:
                printf("\nEnter the Initials : ");
                scanf("%s",&ni);
                search(ni);
                break;


            case 6:
                sort( );
                printf("\n\nSorted");
                break;
            case 7:
                disp();
                break;
        }
        getch();
    }
    getch();
}

Code:

#include<conio.h>
...
#include<dos.h>
...
getch();

Those lines are Windows-specific. conio.h and dos.h are very outdated. Since you're barely using them, remove them. Also, you can use getchar(), which is more portable, in place of getch().

After I made that fix, I compiled your program:

Code:

$ make stud
gcc -Wall -Werror -ggdb3 -std=c99 -pedantic  -lm -lpthread  stud.c   -o stud
stud.c: In function ‘add’:
stud.c:16:9: error: ‘new’ undeclared (first use in this function)
stud.c:16:9: note: each undeclared identifier is reported only once for each function it appears in
stud.c:16:13: error: expected ‘;’ before ‘stud’
stud.c:18:5: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[5]’ [-Werror=format]
stud.c:20:5: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[20]’ [-Werror=format]
stud.c:28:5: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[30]’ [-Werror=format]
stud.c:30:5: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[15]’ [-Werror=format]
stud.c: In function ‘addAt’:
stud.c:54:13: error: ‘stud’ undeclared (first use in this function)
stud.c:54:19: error: expected expression before ‘)’ token
stud.c:56:9: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[5]’ [-Werror=format]
stud.c:58:9: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[20]’ [-Werror=format]
stud.c:66:9: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[30]’ [-Werror=format]
stud.c:68:9: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[15]’ [-Werror=format]
stud.c: In function ‘modAt’:
stud.c:110:23: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[5]’ [-Werror=format]
stud.c:112:23: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[20]’ [-Werror=format]
stud.c:118:23: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[30]’ [-Werror=format]
stud.c:120:23: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[15]’ [-Werror=format]
stud.c: In function ‘search’:
stud.c:134:9: error: implicit declaration of function ‘stricmp’ [-Werror=implicit-function-declaration]
stud.c: At top level:
stud.c:211:1: error: return type defaults to ‘int’ [-Werror]
stud.c: In function ‘main’:
stud.c:250:17: error: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[5]’ [-Werror=format]
cc1: all warnings being treated as errors
make: *** [stud] Error 1

I don't know how you are getting a seg fault, this doesn't even compile. If it compiles for you, you need to turn up the warnings on your compiler, or better yet, get a more current compiler (Dev-C++ is outdated and no longer supported).

As for the problems

• Line 16: You need to pick a language and stick to it. Your code is 99% C, so I would just use C. 'new' is a C++ operator. In C you can use malloc, which is roughly equivalent (you do this on line 54). Also, you must give the full type: struct stud. stud, on it's own, does not exist.
• All the "error: format ‘%s’ expects" errors are because you don't need the & when using an array with scanf. The name of the array (e.g. p->add) is already a pointer to the first element, so adding the & is wrong.
• Line 134: This is not a standard function, maybe it is provided by conio.h or dos.h, I don't know because I don't have those headers. You could write your own very easily however.
• Line 211: You should declare main to explicitly return an int, and then actually return one at the end (see below).

Code:

int main(void)
{
    ...
    return 0;
}

There may be more, but that is plenty for you to work on for now. When you get that finished, and if you still have this seg fault you can't find, then you can come back here for more help. If/when you do so, please provide your updated code along with whatever input causes the seg fault, so we can help you debug.

Originally Posted by Mohamed Sadek

anduril462 i did what you said but the same error appears the code is about student database which contains the student initial name, last name, id, roll no., phone no., address and bate of birth of student all things is ok but when i select the chice no 6 sort records according to initial name the error appears.
i think the error in the sort function and what is the good compiler.
thanks in advance.

Originally Posted by anduril462

When you get that finished, and if you still have this seg fault you can't find, then you can come back here for more help. If/when you do so, please provide your updated code along with whatever input causes the seg fault, so we can help you debug.

Please give new source code, and provide actual input, not just a description of the fields you want. It may be that the names you pick, your birthday format, etc is causing the bug. Don't make me guess at how to replicate this. I can probably find the seg fault in 2 min if you provide the info I asked for.

EDIT: As for compilers, I really like GCC, which is the default for most Linux distributions. A Windows port is also available (called MinGW), and comes with Code::Blocks, an IDE. Another Windows alternative is Pelles C, and even MS Visual C++ has a free version that compiles C code.

anyone can help me the code compile ok but when run and enter data then choose sort records the error appears