newbie structure question...

This is a discussion on newbie structure question... within the C Programming forums, part of the General Programming Boards category; howdy i'm a python/java guy who's going to attempt to pick up C/C++, and so far it's pretty straightforward. I ...

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    newbie structure question...

    howdy

    i'm a python/java guy who's going to attempt to pick up C/C++, and so far it's pretty straightforward. I do have one question regarding structures...

    in all the examples i've seen, when a structure is created, it never initializes the variables to values, it just declares the variable and it's type. is it possible to initialize a variable within a structure when the structure is created?

    here's an example of what i mean:
    Code:
    struct ink {
        char name[60] = "inkedmn";
        int age;
    };
    will that work? (i'm at work and can't test it, i was just curious)

    thanks!
    Last edited by inkedmn; 04-17-2003 at 11:57 AM.
    Brett Kelly

  2. #2
    cereal killer dP munky's Avatar
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    nope, cant initiallize stuff inside of a struct
    guns dont kill people, abortion clinics kill people.

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    Programming Sex-God Polymorphic OOP's Avatar
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    Re: newbie structure question...

    Originally posted by inkedmn
    howdy

    i'm a python/java guy who's going to attempt to pick up C/C++, and so far it's pretty straightforward. I do have one question regarding structures...

    in all the examples i've seen, when a structure is created, it never initializes the variables to values, it just declares the variable and it's type. is it possible to initialize a variable within a structure when the structure is created?

    here's an example of what i mean:
    Code:
    struct ink {
        char name[60] = "inkedmn";
        int age;
    };
    No, however, in C++ you can initialize to default values with constructors.

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    ok, thanks

    is the same true of unions?
    Brett Kelly

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    Registered User Vber's Avatar
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    [QUOTE]Originally posted by inkedmn
    ok, thanks

    is the same true of unions?
    [/QUOTE

    Yes I'm quite sure, I tried jere, and it didn't work.

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    right on, thanks all...

    come to think of it, can anybody give me an example of when it might be appropriate to use a union or structure? AND () when it would be more appropriate to use one or the other (since, to a newb like myself, they appear to be very similar) ?
    Last edited by inkedmn; 04-17-2003 at 12:33 PM.
    Brett Kelly

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    You can initialize a structure by doing the following:
    Code:
    #include <stdio.h>
    
    struct ink {
        char name[60];
        int age;
    };
    
    struct ink ink1 = {
         "HELLO1",
         102	
    };
    
    struct ink ink2 = {
         "HELLO2",
         88	
    };
    
    main()
    {
         printf("%s  %d\n", ink1.name, ink1.age);
         printf("%s  %d\n", ink2.name, ink2.age);
         return 0;
    }

  8. #8
    Just Lurking Dave_Sinkula's Avatar
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    Re: newbie structure question...

    Originally posted by inkedmn
    in all the examples i've seen, when a structure is created, it never initializes the variables to values, it just declares the variable and it's type. is it possible to initialize a variable within a structure when the structure is created?
    You can initialize an object, but not a type.
    Code:
    #include <stdio.h>
    
    struct ink {  /* type */
        char name[60];
        int age;
    };
    
    int main( void )
    {
        struct ink /* type */ svar /* object */ = {"inkedmn"}; /* initializer */
        union {/* type */
            int  i;
            char c;
        } uvar /* object */ = { 42 }; /* initializer */
        printf("svar.name = \"%s\"\n", svar.name);
        printf("uvar.i = %d\n", uvar.i);
        return 0;
    }
    
    /* my output
    svar.name = "inkedmn"
    uvar.i = 42
    */
    A search might turn up some info about structs/unions.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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    ok, so structures seem like very basic classes (i.e., without any behaviours, just attributes). so, something like this...

    Code:
    #include <stdio.h>
    
    struct person {
        char name[25];
        int age;
        char email[35];
    };
    
    struct person inkedmn = {
        "Brett Kelly",
        24,
        "inkedmn@inkedmn.homelinux.org"
    };
    
    int main(void) {
        printf("%s\n%d\n%s\n", inkedmn.name, inkedmn.age, inkedmn.email);
        return (0);
    }
    that's off the top of my head, but does that seem like it would work?
    Last edited by inkedmn; 04-17-2003 at 01:53 PM.
    Brett Kelly

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    Registered User Vber's Avatar
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    it would work

    Fo'sure

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    excellent
    Brett Kelly

  12. #12
    ATH0 quzah's Avatar
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    In C, yes, structures are in essence classes. They're actually just new object types which are typically just a combination of one or more other data types clustered together.

    In C++, structures are exactly the same thing as classes, except that the default access method is public instead of private.

    Quzah.
    Hope is the first step on the road to disappointment.

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    Originally posted by quzah
    In C++, structures are exactly the same thing as classes, except that the default access method is public instead of private.
    i'm a little unclear as to what you mean by the default access method for a structure. is there another method to set structure values beside either using the "constructor" (or whatever the correct name is) or by struct.key = value ? how are those two methods private?

    (not trying to be antagonistic, i'm just curious )
    Brett Kelly

  14. #14
    ATH0 quzah's Avatar
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    I was a bit unclear with my wording. What I mean is:
    Code:
    C++
    
    class myclass
    {
        signed int myvar;
    };
    
    myclass x;
    
    x.myvar = 10; //invalid. myvar is private
    
    struct mystruct
    {
        signed int myvar;
    };
    
    mystruct y;
    
    y.myvar = 10; //valid. myvar is public
    That's what I was trying to illustrate. That is the only difference between classes and structures in C++.

    Quzah.
    Hope is the first step on the road to disappointment.

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    so, are there no access modifiers in C++?

    in Java (my only reference point for C/++ syntax), class members/behaviors have access modifiers, like:

    Code:
    public class JavaClass {
        private int memberInt;
        protected String memberStr;
    
        public static void main(String[] args) {
            System.out.println("Main method");
       }
    }
    so, memberInt would only be available to methods within JavaClass, memberStr is only accessible by JavaClass and it's subclasses, and main can be called by anybody/thing.

    does C/C++ have an equivalent?

    [edit]

    i forgot there's also "protected" class members/behaviours that are accessible only in the same package as the class they exist in (and they're denoted by the absence of an access modifier)
    Last edited by inkedmn; 04-17-2003 at 03:36 PM.
    Brett Kelly

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