"struct" objects with "for-loop" in C Programming

Question

This code is about 'struct' in C..

I created a struct spieler with the properties name and age.. By using the for-loop I let the user to create the struct objects. they are named as sp[i] --> sp1, sp2 etc.

the problem is the objects are created. But I can use them only inside the for-loop. If I want to get the value of "sp1.name" in main function, it doesn't work. How can I solve it?

struct spieler{
  char name[20];
  int age;
};

void erzeuge();

int main() {

int anzahl = 2;
printf("Anzahl Spielern: ");
scanf("%d",&anzahl);

erzeuge(anzahl);

printf("Es sind %d Spielern",anzahl);
/*for(i;i<anzahl;i++){
    printf("%d.%s",i, sp[i].name);
}*/

getchar();

}

void erzeuge(int anzahl){

int i=0;
for(i;i<anzahl;i++){
    struct spieler sp[i];
    printf("Struct fuer Spieler_%d wurde erzeugt\n", i);
    getchar();
    printf("Name: ");
    scanf("%s",sp[i].name);

    printf("%s\n",sp[i].name);
}

You need a global variable/array to access it in main and other functions. Here you create just a local variable. And I personally don't understand what actually does line struct spieler sp[i] - it looks like nonsense to me. Does it even compile? 8-O — Al Kepp
– Al Kepp, Commented Dec 9, 2011 at 23:56
struct spieler sp[i]; declares an array of struct spielers that is i elements long [0,i-1], and sp[i].name accesses element i of it which is an error. — dmckee --- ex-moderator kitten
– dmckee --- ex-moderator kitten, Commented Dec 9, 2011 at 23:58
@AlKepp In C99, it declares a local variable length array of i struct spielers. It compiles, but the array vanishes at the next iteration of the loop. — Daniel Fischer
– Daniel Fischer, Commented Dec 9, 2011 at 23:59
Thanks, Daniel, +1. So it's pretty local array. And it is too short. dmckee +1 — Al Kepp
– Al Kepp, Commented Dec 10, 2011 at 3:09

FreeCodeVN · Accepted Answer · 2011-12-10 00:28:04Z

1

You should declare sp as a pointer at the global scope, and allocate memory for it inside the function erzeuge using malloc.

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

struct spieler {
    char name[20];
    int age;
};

struct spieler *sp;    // Add this

void erzeuge();

int main() {
    int anzahl;
    printf("Anzahl Spielern: ");
    scanf("%d", &anzahl);

    erzeuge(anzahl);

    printf("Es sind %d Spielern\n", anzahl);

    int i;
    for(i = 0; i < anzahl; i++){
        printf("%d.%s\n", i, sp[i].name);
    }

    if (sp) {
        free(sp);
    }
    getchar();
    return 0;
}

void erzeuge(int anzahl) {
    // Add the following line to allocate memory
    sp = (struct spieler*) malloc(anzahl * sizeof(struct spieler));

    int i;
    for (i = 0; i < anzahl; i++) {
        // Remove the following line because it create an array of "i" elements
        // struct spieler sp[i];
        printf("Struct fuer Spieler_%d wurde erzeugt\n", i);
        getchar();
        printf("Name: ");
        scanf("%s",sp[i].name);

        printf("%s\n",sp[i].name);
    }
}

answered Dec 10, 2011 at 0:28

FreeCodeVN

1661 silver badge5 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

kk-dev11 Over a year ago

thanks a lot. It works. <br> but what do you mean by "// Remove the following line because it create an array of "i" elements "?

FreeCodeVN Over a year ago

You used that line to declare the i-th item of the sp array, doesn't it? That's the wrong way. That line will declare a local array (inside the for loop) named sp with total i elements, which means the indexes range from 0 to i-1. By using that line, neither you can access sp from outside of the loop and from main() function nor you can safely access sp[i].

Daniel Fischer · Accepted Answer · 2011-12-09 23:58:04Z

1

You'd have to return an array of players from erzeuge, something like

struct spieler *erzeuge(int anzahl){
    struct spieler *mannschaft = malloc(anzahl*sizeof(struct spieler));
    int i;
    for(i = 0; i < anzahl; ++i){
        // prompt
        scanf("%18s",&mannschaft[i].name);
        ...
    }
    return mannschaft;
}

answered Dec 9, 2011 at 23:58

Daniel Fischer

184k19 gold badges319 silver badges436 bronze badges

Comments

Piotr Praszmo · Accepted Answer · 2011-12-10 00:10:36Z

0

Alternative solution without malloc:

void erzeuge(struct spieler* sp, int anzahl)
{
    ...
}

int main()
{
    int anzahl = 2;

    ...

    struct spieler sp[anzahl];
    erzeuge(sp,anzahl);

    ...
}

answered Dec 10, 2011 at 0:10

Piotr Praszmo

18.4k2 gold badges59 silver badges66 bronze badges

Collectives™ on Stack Overflow

"struct" objects with "for-loop" in C Programming

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related