Problem with array of pointers to structures and such

This is a discussion on Problem with array of pointers to structures and such within the C Programming forums, part of the General Programming Boards category; I have a little problem. In the following problem I am trying to display an array of pointers in a ...

  1. #1
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    Problem with array of pointers to structures and such

    I have a little problem.

    In the following problem I am trying to display an array of pointers in a separate function. The commented section displays the "name" variable correctly, however, the code in display() gives me a funky result with odd letters. Why is that??

    Code:
    static int count = 0;
    typedef struct Record{
            char *name;
            int age;
            float hbp;
            float lbp;
            float riskFactor;
    
    
    } Record;
    static Record *patients[30];
    
    
    void display()
    {
            int k;
            for (k=0;k<count;k++)
            {
                    printf("%d      %s",count, patients[k]->name);
            }
    }
    
    
    
    void enter(){
            patients[count] = (Record *)malloc(sizeof(Record));
            char name[20];
            int age;
            float hbp, lbp;
    
            printf("name: ");
            scanf("%s", name);
            printf("age: ");
            scanf("%d", &age);
            printf("high bp: ");
            scanf("%f", &hbp);
            printf("low bp: ");
            scanf("%f", &lbp);
            patients[count]->name = name;
            patients[count]->age = age;
            patients[count]->hbp = hbp;
            patients[count]->lbp = lbp;
            count++;
    
    //      int k;
    //      for (k=0; k<count;k++)
    //      {
    //              printf("%s", patients[k]->name);
    //      }
    }

  2. #2
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    Code:
    void enter(){
            patients[count] = (Record *)malloc(sizeof(Record));
            char name[20];
    Code:
    patients[count]->name = name;
    The variable "name" is local to enter(); the address of name is NOT valid to use outside of the scope of enter(). You are assigning address on the stack to "patients[count]->name" this is NOT somthing that is save to do.

    Tim S.

  3. #3
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    It's because you are not assigning your string variables correctly...

    Code:
            patients[count]->name = name;
    This isn't going to work because you are not creating a string only copying a pointer to a string and in the end every record will point to the same place...

    You need to do it like this...
    Code:
    typedef struct Record{
            char name[20];
            int age;
            float hbp;
            float lbp;
            float riskFactor;
    } Record;
    Record *patients[30];
    
    // other code...
    
            printf("name: ");
            scanf("%s", patient[count]->name);
            printf("age: ");
            scanf("%d", &patient[count]->age);
            printf("high bp: ");
            scanf("%f", &patient[count]->hbp);
            printf("low bp: ");
            scanf("%f", &patient[count]->lbp);
    Store the actual name buffer in the struct then load the name etc. directly into it.

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    Thanks, it worked! How would I go about clearing the variables then? Since I was more or less doing the same thing.

  5. #5
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    Code:
            Record *temp[30];
            int k;
            count = 0;
            for (k=0;k<count;k++)
            {
                    patients[k]->name = temp[k]->name;
                    patients[k]->age = temp[k]->age;
                    patients[k]->hbp = temp[k]->hbp;
                    patients[k]->lbp = temp[k]->lbp;
            }
    Is what I have, an assignment error?

  6. #6
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    Quote Originally Posted by bungkai View Post
    Thanks, it worked! How would I go about clearing the variables then? Since I was more or less doing the same thing.
    If you use my example there's no need to clear variables... because you are feeding the newly created struct directly.

    If you are worried about garbage as the back end of your string use calloc() instead.

  7. #7
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    Quote Originally Posted by bungkai View Post
    Code:
            Record *temp[30];
            int k;
            count = 0;
            for (k=0;k<count;k++)
            {
                    patients[k]->name = temp[k]->name;
                    patients[k]->age = temp[k]->age;
                    patients[k]->hbp = temp[k]->hbp;
                    patients[k]->lbp = temp[k]->lbp;
            }
    Is what I have, an assignment error?
    Maybe... but it's also unnecessary.

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