accessing struct element from another struct

Hello, I'm not new to programming. I've been developing games with BASIC (FreeBASIC), and Flash games with ActionScript. I even developed a scripting language for beginning programmers to make games.

Now, I decided to learn C to be able to make games for handheld consoles.

I have this code below, where I keep having error message saying:
error: request for member 'value' is something not a structure or union

What I wanted to do is be able to have an array of resizeable strings. I'm aware that there's no String datatype in C. It is why I have char *value in struct Foo. It will serve as my resizeable string in my program.

Now, struct Bar will contain a resizeable array of struct Foo, thus, Foo **foo.

PHP Code:

---

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

typedef struct {
    int etc1;
    char *value;
} Foo;

typedef struct {
    char *etc2;
    Foo **foo;
} Bar;

int main() {
    Bar bar;
    
    bar.foo = (Foo **) malloc(sizeof(Foo) * 2);
        bar.foo[0] = (Foo *) malloc(sizeof(Foo));
        bar.foo[0].value = (char *) malloc(sizeof("howdy"));
            bar.foo[0].value = "howdy";
        
        bar.foo[1] = (Foo *) malloc(sizeof(Foo));
        bar.foo[1].value = (char *) malloc(sizeof("hello world"));
            bar.foo[1].value = "hello world";
    
                printf("bar.foo.value[0] = %s\n", bar.foo[0].value);
                printf("bar.foo.value[1] = %s\n", bar.foo[1].value);
    
        free(bar.foo[0].value);
        free(bar.foo[0]);
        
        free(bar.foo[1].value);
        free(bar.foo[1]);
    
    free(bar.foo);
    
    return 0;
} 


---

In ActionScript, accessing value inside foo would be foo.value. And it follows that accessing foo inside bar would be bar.foo. So I was hoping, I could access value via bar through bar.foo.value. And given that foo is a resizeable array, I was hoping this would work: bar.foo[0].value.

What am I doing wrong? Is this even possible? Or should I declarare a separate Foo object and pass the pointer to it and assign the value?

>Now, struct Bar will contain a resizeable array of struct Foo, thus, Foo **foo.
Shouldn't it be Foo *foo;
You've an error message but which line???

Code:

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                bar.foo[0].value = (char *) malloc(sizeof("howdy"));
                bar.foo[0].value = "hello world";

---

This is not really what you want. You are effectively leaking memory.
I'd suggest you read a good tutorial on C.

oops.

That was just an error in my attempt to simplify what I'm currently working on. It should have been

PHP Code:

---

        bar.foo[0].value = (char *) malloc(sizeof("howdy"));
            bar.foo[0].value = "howdy";
        
        bar.foo[1] = (Foo *) malloc(sizeof(Foo));
        bar.foo[1].value = (char *) malloc(sizeof("hello world"));
            bar.foo[1].value = "hello world"; 


---

Anyway, the error is on all lines trying to access .value.

strcpy is what you need. You cannot assign a string to a location like that, however, you could assign a string literal to a pointer -- but I don't think that's what you want to do.

whoopie! got it! changed .value to ->value.

PHP Code:

---

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

typedef struct {
    int etc1;
    char *value;
} Foo;

typedef struct {
    char *etc2;
    Foo **foo;
} Bar;

int main() {
    Bar bar;
    
    bar.foo = (Foo **) malloc(sizeof(Foo) * 2);
        bar.foo[0] = (Foo *) malloc(sizeof(Foo));
        bar.foo[0]->value = (char *) malloc(sizeof("howdy"));
            bar.foo[0]->value = "howdy";
        
        bar.foo[1] = (Foo *) malloc(sizeof(Foo));
        bar.foo[1]->value = (char *) malloc(sizeof("hello world"));
            bar.foo[1]->value = "hello world";
    
                printf("bar.foo.value[0] = %s\n", bar.foo[0]->value);
                printf("bar.foo.value[1] = %s\n", bar.foo[1]->value);
    
        free(bar.foo[0]->value);
        free(bar.foo[0]);
        
        free(bar.foo[1]->value);
        free(bar.foo[1]);
    
    free(bar.foo);
    
    return 0;
} 


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Quote:

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Originally Posted by Kennedy

strcpy is what you need. You cannot assign a string to a location like that, however, you could assign a string literal to a pointer -- but I don't think that's what you want to do.

---

well, you could. as long as the char pointer has memory allocated of just about the same size of the string value being assigned.

in it's simplest form:

PHP Code:

---

[code]
#include <stdio.h>

int main() {
    char *value = (char *) malloc(sizeof("howdy"));
    value = "howdy";
    printf("%s", value);
}
[/code] 


---

should work. (and it does)

Quote:

---

Originally Posted by Bayint Naung

>Now, struct Bar will contain a resizeable array of struct Foo, thus, Foo **foo.
Shouldn't it be Foo *foo;

---

hmm... let me take a look at it again. thanks for the tip.

Thanks Bayint Naung. I edited the code and it does work with only Foo *foo and not Foo **foo, thus no need to malloc both array instance.

PHP Code:

---

[code]
#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int etc1;
    char *value;
} Foo;

typedef struct {
    char *etc2;
    Foo *foo;
} Bar;

int main() {
    Bar bar;
    
    bar.foo = (Foo *) malloc(sizeof(Foo) * 2);
        bar.foo[0].value = (char *) malloc(sizeof("howdy"));
            bar.foo[0].value = "howdy";
        
        bar.foo[1].value = (char *) malloc(sizeof("hello world"));
            bar.foo[1].value = "hello world";
    
                printf("bar.foo[0].value = %s\n", bar.foo[0].value);
                printf("bar.foo[1].value = %s\n", bar.foo[1].value);
    
        free(bar.foo[0].value);
        
        free(bar.foo[1].value);
    
    free(bar.foo);
    
    return 0;
}[/code] 


---

Thanks Bayint Naung. I edited the code and it does work with only Foo *foo and not Foo **foo, thus no need to malloc both array instance.

PHP Code:

---

[code]
#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int etc1;
    char *value;
} Foo;

typedef struct {
    char *etc2;
    Foo *foo;
} Bar;

int main() {
    Bar bar;
    
    bar.foo = (Foo *) malloc(sizeof(Foo) * 2);
        bar.foo[0].value = (char *) malloc(sizeof("howdy"));
            bar.foo[0].value = "howdy";
        
        bar.foo[1].value = (char *) malloc(sizeof("hello world"));
            bar.foo[1].value = "hello world";
    
                printf("bar.foo[0].value = %s\n", bar.foo[0].value);
                printf("bar.foo[1].value = %s\n", bar.foo[1].value);
    
        free(bar.foo[0].value);
        free(bar.foo[1].value);
    
    free(bar.foo);
    
    return 0;
}
[/code] 


---

Look, you have a memory leak. You are assigning a string literal over a malloced pointer. You are loosing that memory. If you assign a string literal to a pointer, it gets the ADDRESS of that memory, not a strcpy of that memory.

edit:

Code:

---

root@fw03:~# vim test.c
root@fw03:~# gcc -os test.c
root@fw03:~# ./s
st = 80484e0, tmp = 804a008
root@fw03:~# cat test.c
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
        char *st, *tmp;

        st = malloc(100);

        tmp = st;
        st = "Hello World";

        printf("st = %x, tmp = %x\n", st, tmp);
        free(tmp);
        return 0;
}

---

cool!

thanks for correcting me. and for a snippet on testing memory leaks. ;)

thanks.