CODEWITHSUNDEEP
cpointersstructmalloc
mark200
mark200

Reputation: 47

How to allocate memory in struct for char* fields

How to allocate memory for my char * fields in struct ?

My struct: 

   struct student{
    int score;
    char* name;
    char* surname;
};
int main(){
    struct student st[];
    int i;
    int n = 5;
    for(i = 0; i < n; i++){
        printf("Score: \n");
        scanf("%d", &st[i].score);
        printf("Name \n");
        scanf("%s", &st[i].name);
        printf("Surname \n");
        scanf("%s",&st[i].surname)
    }

}

How to malloc to char* name and char* surname ?
I must have an array of struct in form struct student st[].

I don't know, how do this rationally.

void initialise_student( struct student *st, char* name, char* surname)
    {
     st->name = ( strlen( name ) + 1);
     st->surname = (strlen( surname ) +1 );
    }
    int main(){
     int i;
     int n = 5;
     struct student *st[n] = initialise_student();
     for(i = 0; i < n; i++){
       printf("Score: \n");
       scanf("%d", &st[i].score);
       printf("Name \n");
       scanf("%s", &st[i].name);
       printf("Surname \n");
       scanf("%s",&st[i].surname);
      }

How to match this ?

Upvotes: 0

Views: 704

Answers (3)

Florian Weimer
Florian Weimer

Reputation: 33704

If you are already using scanf, you can tell the function to allocate the sting for you by using %ms instead of %s, like this:

char *name;
if (scanf("%ms", &name) != 1) {
    fprintf(stderr, "error: could not read name\n");
    exit(1);
}

EDIT This may not be a valid solution—I forgot that %ms is in POSIX only, not in ISO C.

Upvotes: 0

Vlad from Moscow
Vlad from Moscow

Reputation: 310940

For example

#include <stdlib.h>
#include <string.h>

//...

struct student st[1];
char *name = "Marek";
char *surname = "Piszczaniuk";

st[0].name = malloc( strlen( name ) + 1 );
strcpy( st[0].name, name );

st[0].surname = malloc( strlen( surname ) + 1 );
strcpy( st[0].surname, surname );

st[0].score = 100;

You can write separate functions to set the data members name and surname for an element of the array.

For example

_Bool set_name( struct student *st, const char *name )
{
    st->name = malloc( strlen( name ) + 1 );
    _Bool  success = st->name != NULL;

    if ( success )
    {
        strcpy( st->name, name );
    }

    return success;
}

Upvotes: 3

Bathsheba
Bathsheba

Reputation: 234665

You need to write an initialise_student(struct student* s) function which calls malloc on the char* members. Perhaps this function also takes the name and surname char* pointers of which you take deep copies?

You then call this function with every member of the st array.

Don't forget to build a corresponding free_student(struct student* s) function.

Upvotes: 0

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