CODEWITHSUNDEEP
cpointerslinked-list
s_puria
s_puria

Reputation: 407

C function of linked list wont work

I have function which gets some data from the user, creates a struct using them and adds the struct to a linked list. but it does not save data to the linked list:

typedef struct contact Contact;
typedef Contact *ContactPtr;
int main(){        
    ContactPtr starPtr;
    addContact(starPtr);
    printf("## %s", starPtr->firstName);
    return 0;
}
void addContact(ContactPtr sPtr){
printf("\n FF:\n");
ContactPtr newPtr;
ContactPtr prevPtr;
ContactPtr currentPtr;
newPtr = malloc(sizeof(Contact));
char fN[20];
char sN[20];
char phN[12];
scanf("%s", &fN);
scanf("%s", &sN);
scanf("%s", &phN);

if (newPtr!=NULL){
    strcpy(newPtr->firstName, fN);
    strcpy(newPtr->surName, sN);
    strcpy(newPtr->phoneNo, phN);


    newPtr->next=NULL;
    prevPtr = NULL;
    currentPtr=sPtr;

    while(currentPtr!=NULL){

        prevPtr=currentPtr;
        currentPtr=currentPtr->next;
    }

    if(prevPtr==NULL){
            printf("!!@");
        newPtr->next=sPtr;
        sPtr=newPtr;
    }
    else{
        prevPtr->next=newPtr;
        newPtr->next=currentPtr;
    }
}
else{
printf("$$WRONG");
}
}

Program returns null for starPtr->firstName. Is this problem for the function or the linked list? and is it pointing to the right value?

Upvotes: 1

Views: 87

Answers (1)

alain
alain

Reputation: 12047

In main, you have:

ContactPtr starPtr;
addContact(starPtr);

And addContact is defined as:

void addContact(ContactPtr sPtr){

There is no way how addContact could modify startPtr, that's why it is never pointing to anything useful.

If it would be C++, you could change your code to:

void addContact(ContactPtr& sPtr){

With this, you are passing a reference to startPtr, and it can be modified inside addContact.

But if it is C, you have to use a pointer to a pointer, like

void addContact(ContactPtr* sPtr){

Inside addContact, replace sPtr with *sPtr.

Change main like this:

addContact(&starPtr);

Upvotes: 2

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