printing struct data in a function, while calling using pointers

[Franksy]

hey guys im realy new to programming but am learning fast :) although i think i am going about this the wrong way, im trying to pass information to a function to print structure, i want to use malloc because later on i want to change the code so the user inputs how many "players" and i want to use pointers because we are just starting to learn that at uni,

//structure.h

struct pointsscored
{
    char name[20];
    int goals;
    int behinds;
};

//main.c

#include <stdio.h>
#include <stdlib.h>
#include "structure.h"
void print_data(void *ptr);


int main()
{
    struct pointsscored *ptr;
    int i, numofplayers = 3;


    ptr = (struct pointsscored*) malloc(numofplayers * sizeof(struct pointsscored));


    for(i=0;i<numofplayers;++i)
    {
        printf("Enter name, goals and behinds of player %d (use the space bar to seperate)\n", i+1);
        scanf(" %s%d%d", &(ptr+i)->name, &(ptr+i)->goals, &(ptr+i)->behinds);
    }


    for(i=0;i<numofplayers;++i)
    {
        print_data(ptr);
    }




    system("pause");
    return 0;
}


void print_data(void *ptr)
{
    printf("%s" , ((char)ptr->name));
}

i know im passing to the function wrong so any help at all with anything in my code will be much appreciated. thanks

[Matticus]

For simplicity, I am just going to put everything into a single source file.

#include <stdio.h>
#include <stdlib.h>

struct pointsscored
{
    char name[20];
    int goals;
    int behinds;
};

void print_data(void *ptr);

int main()
{
    struct pointsscored *ptr;
    int i, numofplayers = 3;

    ptr = (struct pointsscored*) malloc(numofplayers * sizeof(struct pointsscored));

    for(i=0;i<numofplayers;++i)
    {
        printf("Enter name, goals and behinds of player %d (use the space bar to seperate)\n", i+1);
        scanf(" %s%d%d", &(ptr+i)->name, &(ptr+i)->goals, &(ptr+i)->behinds);
    }

    for(i=0;i<numofplayers;++i)
    {
        print_data(ptr);
    }

    //system("pause");
    return 0;
}

void print_data(void *ptr)
{
    printf("%s" , ((char)ptr->name));
}

Then compile with full warnings:

main.c||In function 'main':|
main.c|23|warning: format '%s' expects type 'char *', but argument 2 has type 'char (*)[20]'|
main.c||In function 'print_data':|
main.c|37|warning: dereferencing 'void *' pointer|
main.c|37|error: request for member 'name' in something not a structure or union|
||=== Build finished: 1 errors, 2 warnings ===|

I would suggest not working with void pointers in your function parameters as a beginner. Just make your parameter an explicit pointer to the struct type.

Some other notes:

• Check that malloc succeeds before attempting to use that memory.
• When using "scanf" to read a string, you shouldn't include the '&', as an array name by itself acts as a pointer to its first element.
• You don't need to cast malloc: FAQ > Casting malloc - Cprogramming.com
• Whatever memory you allocate, you should free.

Here is a simplified example to illustrate the process:

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

struct struct_str
{
    char s[20];
};

void print_str(struct struct_str *test);

int main(void)
{
    struct struct_str *stest;

    stest = malloc(sizeof(*stest));  /* error checking omitted */

    strcpy(stest->s, "This is a test.");

    print_str(stest);

    free(stest);

    return 0;
}

void print_str(struct struct_str *test)
{
    printf("%s\n", test->s);
}